[2+2]-Photocycloaddition of N-Benzylmaleimide to Alkenes As an Approach to Functional 3-Azabicyclo[3.2.0]heptanes

3-Substituted 6-Azabicyclo[3.1.1]heptanes: Nonclassical Piperidine Isosteres for Drug Discovery

Advanced analogs of piperidine and smaller homologues of tropane─3-substituted 6-azabicyclo[3.1.1]heptanes─were synthesized on a large scale using readily available bulk reagents. The key step of the approach involved the double alkylation reaction of malonate with cis-2,4-bis(mesyloxymethyl)azetidine-1-carboxylate, in turn easily prepared on up to 1 kg scale. After hydrolysis, N-Boc-6-azabicyclo[3.1.1]heptane-3,3-dicarboxylic acid was obtained (up to 400 g in a single run), which was used as a common intermediate for the preparation of all the title building blocks. In particular, Pb(OAc)4-mediated oxidative decarboxylation of this intermediate gave 2,6-methanopiperidone derivative (up to 400 g scale), while monodecarboxylation gave N-Boc-6-azabicyclo[3.1.1]heptane-3-carboxylic acids as an easily separatable mixture of cis and trans diastereomers (up to 100 g scale). Further functional group transformations gave diastereopure cis- and trans-N-Boc-monoprotected diamines and amino alcohols. Molecular structure analysis using exit vector parameters (EVP) revealed that cis isomers of 3-substituted 6-azabicyclo[3.1.1]heptanes are three-dimensional analogs of common 1,4-disubstituted piperidine chair conformer, whereas trans isomers can be considered as unusual "boat" piperidines.

A mild protocol for efficient preparation of functional molecules containing triazole

The construction of a class of novel triazole molecules containing sulfonyl fluoride functionalities was achieved through Cu-catalyzed click chemistry in good to excellent yields. The sulfonyl fluoride moieties were cleaved completely under base conditions to produce N-unsubstituted triazoles quantitatively, which provides a strategy to combine SuFEx click chemistry with Cu-catalyzed click chemistry ingeniously.

Bicyclo[m.n.k]alkane Building Blocks as Promising Benzene and Cycloalkane Isosteres: Multigram Synthesis, Physicochemical and Structural Characterization

Electrophilic double bond functionalization - intramolecular enolate alkylation sequence was used to obtain a series of bridged and fused bicyclo[m.n.k]alkane derivatives (i. e., bicyclo[4.1.1]octanes, bicyclo[2.2.1]heptanes, bicyclo[3.2.1]octanes, bicyclo[3.1.0]hexanes, and bicyclo[4.2.0]heptanes). The scope and limitations of the method were established, and applicability to the multigram synthesis of target bicyclic compounds was illustrated. Using the developed protocols, over 50 mono- and bifunctional building blocks relevant to medicinal chemistry were prepared. The synthesized compounds are promising isosteres of benzene and cycloalkane rings, which is confirmed by their physicochemical and structural characterization (pKa , LogP, and exit vector parameters (EVP)). "Rules of thumb" for the upcoming isosteric replacement studies were proposed.

Chemoselective Reactions of Functionalized Sulfonyl Halides

Chemoselective transformations of functionalized sulfonyl fluorides and chlorides are surveyed comprehensively. It is shown that sulfonyl fluorides provide an excellent selectivity control in their reactions. Thus, numerous conditions are tolerated by the SO2 F group - from amide and ester formation to directed ortho-lithiation and transition-metal-catalyzed cross-couplings. Meanwhile, sulfur (VI) fluoride exchange (SuFEx) is also compatible with numerous functional groups, thus confirming its title of "another click reaction". On the contrary, with a few exceptions, most transformations of functionalized sulfonyl chlorides typically occur at the SO2 Cl moiety.

Photosensitized [2 + 2]-Cycloadditions of Dioxaborole: Reactivity Enabled by Boron Ring Constraint Strategy

A strategy to achieve photosensitized [2 + 2] cycloadditions by means of temporary ring constraint is reported. Specifically, a dioxaborole is prepared that undergoes [2 + 2] cycloadditions with a wide variety of alkenes. This strategy overcomes some challenges with the cycloaddition of acyclic substrates. The products can be easily transformed into cyclobutyl diols or 1,4-dicarbonyl compounds; the latter represents a formal alkene vicinal diacylation. The synthetic utility of this method is shown in the synthesis of valuable heterocycles and biatriosporin D.

Photochemical [2+2] Cycloaddition of Alkynyl Boronates

A photochemical [2+2] cycloaddition of alkynyl boronates and maleimides is reported. The developed protocol provided 35-70 % yield of maleimide-derived cyclobutenyl boronates and demonstrated wide compatibility with various functional groups. The synthetic utility of the prepared building blocks was demonstrated for a range of transformations, including Suzuki cross-coupling, catalytic or metal-hydride reduction, oxidation, and cycloaddition reactions. With aryl-substituted alkynyl boronates, the products of double [2+2] cycloaddition were obtained predominantly. Using the developed protocol, a cyclobutene-derived analogue of Thalidomide was prepared in one step. Mechanistic studies supported the participation of the triplet-excited state maleimides and ground state alkynyl boronates in the key step of the process.

Visible Light-Induced Diastereoselective Construction of Trifluoromethylated Cyclobutane Scaffolds through [2+2]-Photocycloaddition and Water-Assisted Hydrodebromination

A visible light-induced diastereoselective synthesis of trifluoromethylated cyclobutane derivatives is described, consisting of [2+2]-photocycloaddition and water-assisted hydrodebromination by one pot. Quinolinones, isoquinolinones, and coumarins are able to participate in this one-pot process with 1-bromo-1-trifluoromethylethene. In addition, stereodefined trisubstituted trifluoromethylated cyclobutane alcohols, carboxylic acids, and amines can be obtained in a straightforward manner through the ring opening of lactone or lactam without the loss of original high diastereoselectivity given by the water-tristrimethylsilylsilane coordination. The antineoplastic bioactivities of those compounds are also well studied, which exhibit great antineoplastic potential comparable to cisplatin. In the proposed mechanism, thioxanthone (TX) serves as a dual catalyst and a radical chain pathway may be involved in the hydrodebromination process.

Photochemical [2 + 2] Cycloaddition of Alkenes with Maleimides: Highlighting the Differences between N-Alkyl vs N-Aryl Maleimides

Throughout the last 15 years, there has been increased research interest in the use of light promoting organic transformations. [2 + 2] Cycloadditions are usually performed photochemically; however, literature precedent on the reaction between olefins and maleimides is limited to a handful of literature examples, focusing mainly on N-aliphatic maleimides or using metal catalysts for visible-light driven reactions of N-aromatic maleimides. Herein, we identify the differences in reactivity between N-alkyl and N-aryl maleimides. For our optimized protocols, in the case of N-alkyl maleimides, the reaction with alkenes proceeds under 370 nm irradiation in the absence of an external photocatalyst, leading to products in high yields. In the case of N-aryl maleimides, the reaction with olefins requires thioxanthone as the photosensitizer under 440 nm irradiation.

Aqueous Amine-Tolerant [2+2] Photocycloadditions of Unactivated Olefins

The Kochi-Salomon reaction is the only photochemical [2+2] cycloaddition capable of combining two electronically unactivated olefins into a cyclobutane. Yet, the reaction has remained largely unexplored and suffers many drawbacks, most notably an intolerance to Lewis/Brønsted basic amines and amides. Since these groups are ubiquitous in biologically active pharmaceuticals, an amine-tolerant Kochi-Salomon reaction would greatly facilitate rapid exploration of novel drug scaffolds. Herein, we disclose a transformation that is run in water with the most widely available Cu(II) salts and mineral acids. Furthermore, we apply this methodology to synthesize a variety of amine-containing cyclobutanes, including known and novel pharmacological analogues.

Role of an Ice Surface in the Photoreaction of Coumarins

Ice affects many chemical reactions in nature, which greatly influences the atmosphere, climate, and life. However, the exact mechanism of ice in these chemical reactions remains elusive. For example, it is still an open question as to whether ice can act as a catalyst to greatly enhance the reactivity and selectivity, which is essential for the production of some natural compounds in our planet. Here, we discover that ice can lead to high efficiency and stereoselectivity of the [2 + 2] photodimerization of coumarin and its derivatives. The conversion of the [2 + 2] photodimerization of coumarins enhanced by ice is dozens of times higher than that in the unfrozen saturated solution, and the reaction displays a high syn-head-head stereoselectivity (>95%) in comparison with those in the absence of the ice. Note that almost no reaction occurs in the crystal powder and melt of the coumarins, indicating that the role of ice in the photodimerization reaction is not simply due to the usual mechanisms found in the freezing concentration. We further reveal that the reaction rate is found to be proportional to the total area of the ice surface and follows Michaelis-Menten-like kinetics, indicating that the ice surface catalyzes the reaction. Molecular dynamics simulations demonstrate that ice surfaces can induce reactants to form a two-dimensional liquid-crystal-ordered layer with a suitable intermolecular distance and unique side-by-side packing, facilitating stereoselective photodimerization for syn-head-head dimers. These findings give evidence that ice-surface-induced molecular assembly may play an important role in atmospheric heterogeneous photoreaction processes.

A cascade reaction for regioselective construction of pyrazole-containing aliphatic sulfonyl fluorides

A copper-catalyzed cascade reaction of α-diazocarbonyl compounds with ethenesulfonyl fluoride (ESF) is developed, affording a variety of highly functionalized pyrazolyl aliphatic sulfonyl fluorides in good to excellent yields (66-98%). This transformation features broad substrates, exclusive regioselectivity, high atom economy and operational simplicity, thus providing a straightforward method for the direct construction of pyrazole-containing aliphatic sulfonyl fluorides, which will provide great applicable value in medicinal chemistry and other related disciplines.

A photochemical microfluidic reactor for photosensitized [2+2] cycloadditions

Here we report a microfluidic system for photochemical cycloadditions fabricated using silicon micro processing technologies. The system was optimized to yield residence times of just a few minutes for a range of photochemical [2+2]-cycloaddition reactions facilitated using high power UV-LEDs at 375 nm and triplet photosensitizers, which removed the need for the low wavelengths typically required for these types of transformations. Adducts using different excitable olefins with different linear-, carbocyclic- and heterocyclic coupling partners were explored to demonstrate the feasibility of performing photochemistry in microflow in an academic research environment. Finally, a reaction leading to a novel dihydrooxepin-2(3H)-one scaffold, and a mechanistic proposal for its formation are reported.

Intramolecular thiomaleimide [2 + 2] photocycloadditions: stereoselective control for disulfide stapling and observation of excited state intermediates by transient absorption spectroscopy

Thiomaleimides undergo efficient intermolecular [2 + 2] photocycloaddition reactions and offer applications from photochemical peptide stapling to polymer crosslinking; however, the reactions are limited to the formation of the exo head-to-head isomers. Herein, we present an intramolecular variation which completely reverses the stereochemical outcome of this photoreaction, quantitatively generating endo adducts which minimise the structural disturbance of the disulfide staple and afford a 10-fold increase in quantum yield. We demonstrate the application of this reaction on a protein scaffold, using light to confer thiol stability to an antibody fragment conjugate. To understand more about this intriguing class of [2 + 2] photocycloadditions, we have used transient absorption spectroscopy (electronic and vibrational) to study the excited states involved. The initially formed S₂ (π₁π*) excited state is observed to decay to the S₁ (n₁π*) state before intersystem crossing to a triplet state. An accelerated intramolecular C–C bond formation provides evidence to explain the increased efficiency of the reaction, and the impact of the various excited states on the carbonyl vibrational modes is discussed.

Tethered bromomaleimides are described which undergo thiol conjugation and rapid regio- and stereoselective photocycloadditions to serve as disulfide staples; with the excited state intermediates observed by transient absorption spectroscopies.

Application of Industrially Relevant HydroFluoroOlefin (HFO) Gases in Organic Syntheses

Hydrofluoroolefin (HFO) gases are state-of-the-art cooling agents with widespread household and industrial applications. Considering their structural benefits these fluorous feedstocks have gained the attention of organic chemists in the last couple of years. In this short review we summarized the existing synthetic transformations of these gaseous starting material and present their applicability in the synthesis of fluorine-containing organic molecules, which have potential importance as building blocks and reagents for diverse syntheses.

1 Introduction

2 Addition Reactions

3 Substitutions

4 Organometallic Chemistry

4.1 Organolithium Compounds

4.2 Organometallic Complexes

4.3 Silicon Organic Chemistry

4.4 Boron Organic Chemistry

4.5 Palladium-Catalyzed Transformations

4.6 Metathesis

4.7 Hydroesterification, Hydroformylation

5 Conclusions

Large-Scale Synthesis and Modifications of Bicyclo[1.1.1]pentane-1,3-dicarboxylic Acid (BCP)

In flow photochemical addition of propellane to diacetyl allowed construction of the bicyclo[1.1.1]pentane (BCP) core in a 1 kg scale within 1 day. Haloform reaction of the formed diketone in batch afforded bicyclo[1.1.1]pentane-1,3-dicarboxylic acid in a multigram amount. Representative gram scale transformations of the diacid were also performed to obtain various BCP-containing building blocks—alcohols, acids, amines, trifluoroborates, amino acids, etc.—for medicinal chemistry.

Bicyclic Pyrrolidines for Medicinal Chemistry via [3 + 2]-Cycloaddition

A general approach to bicyclic fused pyrrolidines via [3 + 2]-cycloaddition between nonstabilized azomethyne ylide and endocyclic electron-deficient alkenes was elaborated. "Push-pull" alkenes and CF₃-alkenes did not react with the azomethyne ylide under the previously reported conditions, and we developed a superior protocol (LiF, 140 °C, no solvent). Among obtained products were medchem-relevant bicyclic sulfones, monofluoro-, difluoro-, and trifluoromethyl-substituted pyrrolidines. This approach not only allowed preparation of novel molecules but also significantly simplified synthesis of the existing ones (e.g., sofinicline).

Acetylene and Ethylene: Universal C2 Molecular Units in Cycloaddition Reactions

Acetylene and ethylene are the smallest molecules that contain an unsaturated carbon–carbon bond and can be efficiently utilized in a large variety of cycloaddition reactions. In this review, we summarize the application of these C2 molecular units in cycloaddition chemistry and highlight their amazing synthetic opportunities.

1 Introduction

2 Fundamental Features and Differences of Cycloaddition Reactions Involving Acetylene and Ethylene

3 (2+1) Cycloaddition

4 [2+2] Cycloaddition

5 (3+2) Cycloaddition

6 [4+2] Cycloaddition

7 (2+2+1) Cycloaddition

8 [2+2+2] Cycloaddition

9 The Use of Acetylene and Ethylene Cycloaddition for Deuterium and 13C Labeling

10 Conclusions

Photocatalyzed Intramolecular [2+2] Cycloaddition of N-Alkyl-N-(2-(1-arylvinyl)aryl)cinnamamides

N-Alkyl-N-(2-(1-arylvinyl)aryl)cinnamamides are converted into natural product inspired scaffolds via iridium photocatalyzed intramolecular [2+2] photocycloaddition. The protocol has a broad substrate scope, whilst operating under mild reaction conditions. Tethering four components forming a trisubstituted cyclobutane core builds rapidly high molecular complexity. Our approach allows the design and synthesis of a variety of tetrahydrocyclobuta[c]quinolin-3(1H)-ones, in yields ranging between 20-99 %, and with excellent regio- and diastereoselectivity. Moreover, it was demonstrated that the intramolecular [2+2]-cycloaddition of 1,7-enynes-after fragmentation of the cyclobutane ring-leads to enyne-metathesis-like products.

Bicyclic Piperidines via [2 + 2] Photocycloaddition

A synthetic strategy to fused bicyclic piperidines-building blocks for medicinal chemistry-is developed. The key step was an intramolecular [2 + 2]-photocyclization. The photochemical step was performed on a gram scale. Crystallographic analysis of the obtained compounds revealed that they occupy a novel chemical space and can be considered as elongated analogues of 3-substituted piperidines.

Visible light-induced one-pot synthesis of CF3/CF2-substituted cyclobutene derivatives

An efficient one-pot approach for the controllable synthesis of trifluoromethyl/gem-difluoromethylene substituted cyclobutene derivatives has been developed. The mechanism may involve visible light-induced [2+2]-cycloaddition of quinolinones with 1-bromo-1-trifluoromethylethene, followed by base-promoted dehydrobromination, [1,3]-H shift and further dehydrofluorination. A variety of CF3/CF2-substituted cyclobutenes that are currently difficult to obtain are afforded in good yields in this protocol, which may find its way into future fluorinated cyclobutene preparation.

Fsp3: A new parameter for drug-likeness

The drug-likeness of a compound is a key factor during the initial phases of drug discovery. It can be defined as the similarity between compounds and drugs. Here, we collate research related to the fraction of sp³ carbon atoms (Fsp³), including related high-throughput screening (HTS) cases, structural modifications based on Fsp³, and strategies to improve it. We also introduce new synthetic methods for spirocyclic scaffolds. It is likely that the reasonable rigidity of spirocyclic scaffolds will provide a new generation of drug candidates.

Photochemical [2 + 2] Cycloaddition of Alkenyl Boronic Derivatives: An Entry into 3-Azabicyclo[3.2.0]heptane Scaffold

The synthesis of 3-azabicyclo[3.2.0]heptyl boropinacolates and trifluoroborates via the [2 + 2] photocycloaddition of the corresponding alkenyl boronic derivatives and maleimides or maleic anhydride is described. Optimization of the reaction conditions (i.e., wavelength, concentration of the reagents, photosensitizer) was carried out, and the scope and limitations of the method were studied. Alkenyl boronic acid pinacolates were found to be more suitable for the [2 + 2] cycloaddition, providing better reaction outcomes compared to the trifluoroborates. The utility of this approach was shown by the preparation of bi- and trifunctional building blocks (21 examples), which could be easily synthesized on up to 60 g scale. These cycloadducts provide a convenient entry into the 3-azabicyclo[3.2.0]heptane scaffold through the C-C coupling or oxidative deborylation reactions.

Building the Housane: Diastereoselective Synthesis and Characterization of Bicyclo[2.1.0]pentane Carboxylic Acids

An approach to 1,3-disubstitued bicyclo[2.1.0]pentane (housane) derivatives was developed. The method relied on lithium bis(trimethylsilyl)amide-mediated intramolecular cyclization of trisubstitued cyclopentane carboxylates bearing a leaving group (at the C-4 position) and an additional substituent (at the C-3 atom), in turn synthesized from cyclopent-3-ene carboxylate. The synthetic sequence allowed for the preparation of both cis- and trans-1,3-disubstituted housane-1-carboxylic acids in diastereoselective manner on up to 80 g scale. In particular, bicyclic γ-amino acids-γ-aminobutyric acid analogues-were synthesized. It was shown that the bicyclo[2.1.0]pentane did not significantly affect pK_a of the corresponding derivatives and slightly increased their hydrophilicity (by 0.07-0.25 Log P units) as compared to cyclopentane. X-ray diffraction studies showed that cis- and trans-1,3-disubstituted housanes can be considered as flattened analogues of the corresponding cyclopentane derivatives with fixed envelope conformation of the five-membered ring.

Light-induced [2 + 2] cycloadditions for the construction of cyclobutane-fused pyridinyl sulfonyl fluorides

A photocatalytic [2 + 2] cycloaddition between pyridones or isoquinolones and ethenesulfonyl fluoride was achieved, generating unique cyclobutane-fused pyridinyl sulfonyl fluoride compounds.

Escaping from Flatland: [2 + 2] Photocycloaddition; Conformationally Constrained sp3-rich Scaffolds for Lead Generation

Pressure on researchers to deliver new medicines to the patient continues to grow. Attrition rates in the research and development process present a significant challenge to the viability of the current model of drug discovery. Analysis shows that increasing the three-dimensionality of potential drug candidates decreases the risk of attrition, and it is for this reason many workers have taken a new look at the power of photochemistry, in particular photocycloadditions, as a means to generate novel sp³-rich scaffolds for use in drug discovery programs. The viability of carrying out photochemical reactions on scale is also being addressed by the introduction of new technical developments.

Far Away from Flatland. Synthesis and Molecular Structure of Dihetera[3.3.n]propellanes and Trihetera[3.3.n]propellanes: Advanced Analogues of Morpholine/Piperazine

An approach to di- and trihetera[3.3.n]propellanes (n = 2-4 ), advanced morpholine and piperazine analogues, is developed. The key step of the reaction sequence included a [3 + 2] cycloaddition reaction of unsaturated vicinal dicarboxylic acid derivatives and in situ generated azomethine ylide resulting in the formation of the pyrrolidine ring. One more heteroaliphatic ring (i.e., pyrrolidine or tetrahydrofuran) was annelated by nucleophilic cyclization of the appropriate 1,4-dielectrophilic intermediates. There were 11 examples of the title products obtained in 3-5 steps on a multigram scale with 10-72% overall yields. Additionally, molecular structures of homologous dihetera[3.3.n]propellanes, analogues of morpholine, were obtained from X-ray diffraction studies and analyzed using exit vector plots (EVPs). It was shown that the scaffolds obtained are somewhat larger as compared to the parent morpholine and bicyclic 3-oxa-7-azabicyclo[3.3.0]octane. Moreover, despite very similar chemical structures, they provide a very distinct spatial position of heteroatoms, which is clearly seen from the conformation adopted by a formal eight-membered ring including both N and O atoms (i.e., crown, boat-chair, twist chair-chair, and boat-boat for the oxaza[3.3.2]-, -[3.3.3]-, -[4.3.3]propellanes, and 3-oxa-7-azabicyclo[3.3.0]octane, respectively).

The Symbiotic Relationship Between Drug Discovery and Organic Chemistry

All pharmaceutical products contain organic molecules; the source may be a natural product or a fully synthetic molecule, or a combination of both. Thus, it follows that organic chemistry underpins both existing and upcoming pharmaceutical products. The reverse relationship has also affected organic synthesis, changing its landscape towards increasingly complex targets. This Review article sets out to give a concise appraisal of this symbiotic relationship between organic chemistry and drug discovery, along with a discussion of the design concepts and highlighting key milestones along the journey. In particular, criteria for a high-quality compound library design enabling efficient virtual navigation of chemical space, as well as rise and fall of concepts for its synthetic exploration (such as combinatorial chemistry; diversity-, biology-, lead-, or fragment-oriented syntheses; and DNA-encoded libraries) are critically surveyed.

Photocycloaddition of S,S-Dioxo-benzothiophene-2-methanol, Reactivity in the Solid State and in Solution: Mechanistic Studies and Diastereoselective Formation of Cyclobutyl Rings

The formation of cyclobutane rings is a promising strategy in the development of potential drugs and/or synthetic intermediates, typically challenging to obtain due to their constrained nature. In this work, the [2 + 2] photocycloaddition reaction of S,S-dioxobenzothiophene-2-methanol was explored in microcrystalline powders and its outcome was compared to that observed in solution. It was found that the molecular constraints inherited within the crystal lattice provide an optimal environment that leads to photodimer 4 as the major product in ca. 9.6:0.4 diastereomeric ratios with conversions >95%. The photoreaction was analyzed via X-ray, displaying a crystalline-to-amorphous transformation and showing that units of monomer 2 align to generate the corresponding dimer with a syn-head-to-tail regio- and diastereoselectivity. This result contrasted with that obtained in solution, where the diastereomeric ratio varied as a function of the excited state that is generated, to yield mixtures of dimers 4 and 5 (anti-head-to-tail), or exclusively 5 in the triplet-sensitized photoreaction, in the presence of benzophenone. Density functional theory was used to elucidate a plausible detailed mechanism for the phototransformation, which aided in justifying the results that led to the corresponding dimers. X-ray crystallography allowed us to establish the stereochemical assignment of the obtained cyclobutyl rings. Thus, the use of solid-state or solution photochemistry can be used to gain control of diastereo- and regioselectivities in the formation of this important moiety.

Sequential Photochemical and Prins Reactions for the Diastereoselective Synthesis of Tricyclic Scaffolds

Cyclobutene alcohols undergo Prins cyclisations to generate single diastereomers of novel tricyclic heterocycles with five contiguous stereocentres. The reaction times are significantly shorter (ca. 15 min) than with traditional alkene substrates. Stereoselective aza-Prins cyclisations of cyclobutene amine derivatives give fused aza-heterocyclic scaffolds. Computational studies provide insight into the observed stereocontrol. The modular approach is flexible, enabling the introduction of a variety of functional groups (including amides, nitriles, alkynes, and arenes) into the sp³ -rich heterocyclic scaffolds.

Scalable Synthesis of Biologically Relevant Spirocyclic Pyrrolidines

Synthetic approaches toward multigram preparation of spirocyclic α,α-disubstituted pyrrolidines from readily available starting materials are discussed. It was shown that although a number of synthetic methodologies have been known to date, many of the title compounds remain hardly accessible. The most appropriate literature method (which relied on reaction of imines and allyl magnesium halide, followed by bromocyclization) was identified and optimized. It was found that the method is most fruitful for simple non-functionalized substrates. Two novel approaches based on the Sakurai or Petasis reactions of cyclic ketones, followed by hydroboration-oxidation at the allyl moiety thus introduced, were elaborated. The latter method had the largest scope and was beneficial for the substrates containing organosulfur or protected amino functions. For the synthesis of 4-azaspiro[2.4]heptane, an alternative synthetic scheme commencing from tert-butyl cyclopropanecarboxylate (instead of the corresponding ketone) was developed. It was shown that the whole set of the methodologies developed can be used for the synthesis of various spirocyclic α,α-disubstituted pyrrolidines-advanced building blocks of potential importance to medicinal and agrochemistry-at up to a 100 g scale.