Spirocyclic β-Lactams: Synthesis and Biological Evaluation of Novel Heterocycles

Copper-Catalyzed Asymmetric Kinugasa/Michael Addition Cascade Reactions for the Synthesis of Chiral Spiro β-Lactams

A mild copper-catalyzed asymmetric Kinugasa/Michael addition cascade process is developed. The reaction of α, β-unsaturated ester-tethered propiolamides with nitrones provides an efficient protocol for the construction of functionalized chiral 2,6-diazaspiro[3.4]octane-1,5-dione products in satisfactory yields and with high enantio- and diastereoselectivities.

Rapid Access to Chiral Spiro[2.3] Lactams: Stereoselective Hydroborylation and Hydrosilylation and Remote Control of Axial Chirality by Copper-Catalyzed Desymmetrization of Spirocyclopropenes

Chiral spirocyclopropyl β-lactams are common motifs in bioactive compounds and pharmaceuticals. Here we disclose a diastereoselective and enantioselective hydroborylation and hydrosilylation of spirocyclopropenes, via a Cu-catalyzed desymmetrization strategy, for the rapid preparation of enantio-enriched spirocyclopropyl β-lactams. The efficient desymmetrization strategy allows the remote control of axial chirality, offering the borylated and silylated products bearing central, spiro, and axial chirality. The combination of multichiral elements would provide a novel motif for biological evaluation in potential drug discovery.

Variable-Sized bis(4-spiro-fused-β-lactam)-Based Unsaturated Macrocycles: Synthesis and Characterization

The synthesis with structural identifications including NMR and HRMS spectral data along with single-crystal X-ray diffraction analysis (for 20b, 23b, 25b-27b) of a family of 14 new syn/anti bis-4-spiro-β-lactam-based unsaturated macrocycles (19a,b-27a,b), obtained by multistep synthesis including (i) diimine formation, (ii) Staudinger [2 + 2] ketene-imine cycloaddition, and (iii) ring-closing metathesis (RCM), is reported.

Sequential Diimination, Staudinger [2 + 2] Ketene-Imine Cycloaddition, and Ring-Closing Metathesis (RCM) Reactions: In Route to Bis(4-spiro-fused-β-lactams)-Based Macrocycles

Based on sequential organic transformations, that is, diimine formation, Staudinger [2 + 2] ketene-imine cycloaddition, and ring-closing metathesis (RCM) reactions, the synthesis with full structural identification including NMR and HRMS spectral data along with single X-ray diffraction analysis (for anti 7b, anti 8b, syn 9a, and anti 9b) of the first syn/anti bis-4-spiro-β-lactams-based azacrown ethers (7a,b-9a,b) is reported.

1,3-Dipolar cycloaddition of nitrones: synthesis of multisubstituted, diverse range of heterocyclic compounds

The 1,3-dipolar cycloaddition reaction of nitrone is one of the most important methods for the synthesis of different sizes of heterocycles which have enormous applications in natural products, biologically active molecules and pharmaceuticals.

Evaluation of benzthiazolidine-based formamidinium salts for the synthesis of penem-type β-lactams by uncatalysed carbonylation of acyclic diaminocarbenes

The reaction of [iPr2N=CHCl]Cl with 2-phenylbenzthiazolidine (Ph-BtzH) and subsequent anion metathesis afforded the formamidinium salt [(Ph-Btz)CH(NiPr2)][PF6] ([1aH][PF6]). The reaction of [1aH][PF6] with (Me3Si)2NNa in the presence of grey selenium furnished the selenourea derivative 1aSe as trapping product of the acyclic diaminocarbene 1a. In the absence of selenium, a 2H-1,4-benzothiazine derivative (2) was obtained, which is an isomer of 1a, whose formation is plausibly initiated by deprotonation of [1aH]+ not at the cationic N2CH unit, but at the neighbouring PhCH position. CO was ineffective as trapping reagent for 1a. [1aH][PF6], 1aSe and 2 have been structurally characterised by X-ray diffraction.

Stable and Persistent Acyclic Diaminocarbenes with Cycloalkyl Substituents and Their Transformation to β-Lactams by Uncatalysed Carbonylation with CO

Four new acyclic diaminocarbenes (ADACs), viz. [(cyclo-C_n H_2n-1 )₂ N]₂ C (n=5-7) and iPr₂ N-C-N(cyclo-C₆ H₁₁ )₂ , were synthesised by reacting the corresponding formamidinium hexafluorophosphates with NaN(SiMe₃ )₂ . Their nucleophilicities and electrophilicities were respectively judged from the ¹ J_CH values determined for the N₂ CH unit of the corresponding formamidinium cations and from the ⁷⁷ Se NMR chemical shifts of the selenourea derivatives obtained from the reaction of elemental selenium with the corresponding ADACs. An ambiphilic profile essentially identical to that of the "Alder carbene" (iPr₂ N)₂ C was found in each case. Similar to the latter carbene, the new ADACs undergo a well-defined thermal decomposition by β-fragmentation, affording an alkene and a formamidine. The stabilities of [(cyclo-C_n H_2n-1 )₂ N]₂ C depend strongly on the value of n, following the order 6>5>7, with the latter congener being too unstable for isolation. [(cyclo-C₆ H₁₁ )₂ N]₂ C shows no thermal decomposition at room temperature in solution and is thus significantly more stable than (iPr₂ N)₂ C. The stability of iPr₂ N-C-N(cyclo-C₆ H₁₁ )₂ is intermediate between that of (iPr₂ N)₂ C and [(cyclo-C₆ H₁₁ )₂ N]₂ C, its β-fragmentation selectively affording propene and iPrN=CH-N(cyclo-C₆ H₁₁ )₂ . [(cyclo-C_n H_2n-1 )₂ N]₂ C (n=5-7) react readily with CO under mild conditions, selectively affording trisubstituted spirocyclic β-lactam derivatives with an antimicrobial activity spectrum similar to that of penicillin G.

Diversity-Oriented Synthesis and Chemoinformatic Analysis of the Molecular Diversity of sp3-Rich Morpholine Peptidomimetics

Diversity-Oriented Synthesis (DOS) consists of generating structurally diverse compounds from a complexity-generating reaction followed by cyclization steps and appendage diversity. DOS has gathered interest to systematically explore the chemical space by generating high-quality small-molecule collections as probes to investigate biological pathways. The generation of heterocycles using amino acid and sugar derivatives as building blocks is a powerful approach to access chemical and geometrical diversity thanks to the high number of stereocenters and the polyfunctionality of such compounds. Our efforts in this field are focused on the generation of diversity-oriented molecules of peptidomimetic nature as a tool addressing protein-protein interactions, taking advantage of amino acid- and sugar-derived polyfunctional building blocks to be applied in couple-pair synthetic approaches. In this paper, the combination of diversity-oriented synthesis and chemoinformatics analysis of chemical space and molecular diversity of heterocyclic peptidomimetics are reported, with particular interest toward carbohydrate- and amino acid-derived morpholine scaffolds with a higher fraction of sp3 carbon atoms. Also, the chemoinformatic analysis of chemical space and molecular diversity of 186 morpholine peptidomimetics is outlined.

Ring Rearrangement Metathesis in 7-Oxabicyclo[2.2.1]heptene (7-Oxanorbornene) Derivatives. Some Applications in Natural Product Chemistry

Metathesis reactions is firmly established as a valuable synthetic tool in organic chemistry, clearly comparable with the venerable Diels-Alder and Wittig reactions and, more recently, with the metal-catalyzed cross-coupling reactions. Metathesis reactions can be considered as a fascinating synthetic methodology, allowing different variants regarding substrate (alkene and alkyne metathesis) and type of metathetical reactions. On the other hand, tandem metathesis reactions such Ring Rearrangement Metathesis (RRM) and the coupling of metathesis reaction with other reactions of alkenes such as Diels-Alder or Heck reactions, makes metathesis one of the most powerful and reliable synthetic procedure.

In particular, Ring-Rearrangement Metathesis (RRM) refers to the combination of several metathesis transformations into a domino process such as ring-opening metathesis (ROM)/ring-closing metathesis (RCM) and ROM-cross metathesis (CM) in a one-pot operation. RRM delivers complex frameworks that are difficult to assemble by conventional methods constitutingan atom economic process. RRM is applicable to mono- and polycyclic systems of varying ring sizes such as cyclopropene, cyclobutene, cyclopentene, cyclohexene, pyran systems, bicyclo[2.2.1]heptene derivatives, bicyclo[2.2.2]octene derivatives, bicyclo[3.2.1]octene derivatives and bicyclo[3.2.1]octene derivatives.

In this review our attention has focused on the RRM reactions in 7-oxabicyclo[2.2.1]heptene derivatives and on their application in the synthesis of natural products or significant subunits of them.

N-aryl lactams by regioselective ozonation of N-aryl cyclic amines

Ozonation of N-aryl-cyclic amines in organic solvents gave N-aryl-lactams regioselectively. In particular, 4-(4-aminophenyl)-morpolin-3-one, a key intermediate in the preparation of factor Xa inhibitors, was obtained in fair yields. The method represents an alternative approach for the lactamization of tertiary N-arylic substrates and is based on a “metal-free” introduction of the carbonyl function into the heterocyclic ring.