Facile preparation of allylzinc species from allylboronates and zinc amide via a boron-to-zinc exchange process and their reactions with carbonyl compounds, imines and hydrazones

Amine adducts of triallylborane as highly reactive allylborating agents for Cu(I)-catalyzed allylation of chiral sulfinylimines

The implementation of selective catalytic processes with highly active reagents is an attractive strategy that meets the modern principles of sustainable development of chemistry. In the current study, we for the first time describe the method and general principles of Cu(I)-catalyzed allylation of imines with amine adducts of allylic triorganoboranes. Triallylborane is an extremely reactive compound and cannot be used for the catalytic allylation of imines, whereas its amine adducts are ideal substrates for catalysis. The structure of the amine fragment successfully balances the safety, selectivity and stability of the allylboron reagent, allowing it to demonstrate high activity in catalytic allylation reactions, exceeding many times any known allylboranes. The obtained results are supported by quantitative kinetics data and DFT calculations. The catalytic efficacy of the system was demonstrated on model sulfinylimines (23 examples). High diastereoselectivity up to >99% was achieved, including for the gram-scale synthesis of 2-hydroxyphenyl-derivatives. Taking into account the high reactivity and unsurpassed atom-economy of amine adducts of triallylborane (AAT), they can be considered as prospective allylation reagents with Cu(I) and other appropriate metallocatalysts.

Nitrogen-Doped Carbon-Incarcerated Zinc Electrodes as Heterogeneous Catalysts for Electrochemical Allylation of Carbonyl Compounds

Electrochemical allylation reactions of carbonyl compounds using cathodes prepared from nitrogen-doped carbon (NDC)-incarcerated zinc catalysts have been developed. A range of aldehydes and ketones afforded the desired allylic alcohols in high yields with <10 mol % zinc leaching, and the heterogeneous nature of the active species was suggested. Compared with bulk zinc electrodes, NDC-stabilized zinc nanoparticle species were compatible with a broader range of heteroaromatic substrates and enabled the use of an undivided cell.

Dienylation of N-benzoylhydrazones with CF3-substituted homoallenylboronates in water

A convenient method for the dienylation of N-benzoylhydrazones in water has been developed. This protocol expanded the synthetic application of functionalized homoallenylboronates to provide the useful 2-aminomethyl-1,3-diene derivatives with high efficiency (up to 99% yield) and stereoselectivity without using any catalyst, additive or inert atmosphere. Furthermore, the transformation of a 2-aminomethyl-1,3-diene derivative to synthesize a functionalized pyrrolidine derivative was also explored.

Bi(OAc)3/Chiral Phosphoric Acid-Catalyzed Enantioselective 1,2- and Formal 1,4-Allylation Reaction of β,γ-Unsaturated α-Ketoesters

A highly efficient asymmetric 1,2-allylation reaction of β,γ-unsaturated α-ketoesters was realized by using a Bi(OAc)₃/chiral phosphoric acid catalyst system under mild conditions. Meanwhile, using this combined strategy of enantioselective 1,2-allylation and subsequent anionic oxy-Cope rearrangement, the asymmetric formal 1,4-allylation reaction was achieved by a one-pot process. These reactions offer rapid access to an array of homoallylic tertiary alcohols and γ-allyl-α-ketoesters with good yields and excellent enantioselectivities. Density functional theory calculations were conducted to interpret the high enantioselectivity.

Diastereo- and Enantioselective Synthesis of 3-Allyl-3-hydroxyoxindoles via Allylation of Isatins

A highly diastereo- and enantioselective allylation of isatins with 3-substituted allylboronic compounds was achieved by the chiral N,N'-dioxide/Lu(OTf)₃ complex. This approach provides an efficient route to useful enantioenriched 3-allyl-3-hydroxyoxindoles with adjacent tetrasubstituted tertiary or tetrasubstituted quaternary stereogenic centers. Density functional theory calculations were performed to understand the different diastereoselection between the background reaction and catalytic process. Moreover, allylation with potassium allyltrifluoroborate was accomplished by the chiral N,N'-dioxide/In(OTf)₃ complex. The synthetic utility was demonstrated by further transformation of the product to a tetrahydrofuranyl oxindole derivative.

Organocatalytic Synthesis of α-Triphenylmethylamines from Diarylketimines and Phenols

A formal Betti reaction between variously substituted phenols and benzophenone-derived imines to afford α-triphenylmethylamines is reported. The key to the success of this transformation is the in situ generation of the reactive benzophenone iminium species under organocatalytic conditions. Different phenols reacted smoothly, enabling the synthesis of an array of α-triphenylmethylamines, which are highly valued structural motifs in bioactive molecules and chemical sensors.

Copper(I)-catalyzed asymmetric 1,6-conjugate allylation

Catalytic asymmetric conjugate allylation of unsaturated carbonyl compounds is usually difficult to achieve, as 1,2-addition proceeds dominantly and high asymmetric induction is a challenging task. Herein, we disclose a copper(I)-NHC complex catalyzed asymmetric 1,6-conjugate allylation of 2,2-dimethyl-6-alkenyl-4H-1,3-dioxin-4-ones. The phenolic hydroxyl group in NHC ligands is found to be pivotal to obtain the desired products. Both aryl group and alkyl group at δ-position are well tolerated with the corresponding products generated in moderate to high yields and high enantioselectivity. Moreover, both 2-substituted and 3-substituted allylboronates serve as acceptable allylation reagents. At last, the synthetic utility of the products is demonstrated in several transformations by means of the versatile terminal olefin and dioxinone groups.

Catalytic asymmetric conjugate allylation of unsaturated carbonyl compounds is usually difficult to achieve due to competing 1,2-addition. Here, the authors report a copper(I)-catalyzed asymmetric 1,6-conjugate allylation of 2,2-dimethyl-6-alkenyl-4H-1,3-dioxin-4-ones with good scope and high enantioselectivity.

Bi(OAc)3/chiral phosphoric acid catalyzed enantioselective allylation of isatins

Herein, we disclosed an efficient protocol for the construction of chiral 3-allyl-3-hydroxyoxindoles via the enantioselective allylation reaction of isatins and allylboronates catalyzed by a simple binary acid Bi(OAc)₃/CPA system under mild conditions.

Development of a Simple Adjustable Zinc Acid/Base Hybrid Catalyst for C-C and C-O Bond-Forming and C-C Bond-Cleavage Reactions

A newly designed zinc Lewis acid/base hybrid catalyst was developed. By adjusting the Lewis acidity of the zinc center, aldol-type additions of 2-picolylamine Schiff base to aldehydes proceeded smoothly to afford syn-aldol adduct equivalents, trans-N,O-acetal adducts, in high yields with high selectivities. NMR experiments, including microchanneled cell for synthesis monitoring (MICCS) NMR analysis, revealed that anti-aldol adducts were formed at the initial stage of the reactions under kinetic control, but the final products were the trans-(syn)-N,O-acetal adducts that were produced through a retro-aldol process under thermodynamic control. In the whole reaction process, the zinc catalyst played three important roles: i) promotion of the aldol process (C-C bond formation), ii) cyclization process to the N,O-acetal product (C-O bond formation), and iii) retro-aldol process from the anti-aldol adduct to the syn-aldol adduct (C-C bond cleavage and C-C bond formation).

Practical and Broadly Applicable Catalytic Enantioselective Additions of Allyl-B(pin) Compounds to Ketones and α-Ketoesters

A set of broadly applicable methods for efficient catalytic additions of easy-to-handle allyl-B(pin) (pin=pinacolato) compounds to ketones and acyclic α-ketoesters was developed. Accordingly, a large array of tertiary alcohols can be obtained in 60 to >98 % yield and up to 99:1 enantiomeric ratio. At the heart of this development is rational alteration of the structures of the small-molecule aminophenol-based catalysts. Notably, with ketones, increasing the size of a catalyst moiety (tBu to SiPh3 ) results in much higher enantioselectivity. With α-ketoesters, on the other hand, not only does the opposite hold true, since Me substitution leads to substantially higher enantioselectivity, but the sense of the selectivity is reversed as well.

Zinc Amide Catalyzed Regioselective Allenylation and Propargylation of Ketones with Allenyl Boronate

Zinc amide catalyzed, regioselective allenylation and propargylation of ketones with allenyl boronate is reported. Tertiary allenyl and homopropargyl alcohols were obtained, respectively, in high selectivities, from the same starting materials, simply by changing the reaction conditions. The substrate scope was wide. Mechanistic studies suggest that the reactions are controlled under kinetic and thermodynamic conditions.

Tertiary α-diarylmethylamines derived from diarylketimines and organomagnesium reagents

Organomagnesium reagents enable swift and versatile derivatisation of diarylimines to the corresponding α-substituted diarylmethylamines in excellent yields, through fast and clean reactions.

Catalytic asymmetric allylation of carbonyl compounds and imines with allylic boronates

Enantioselective allylation is a highly used organic reaction to prepare chiral homoallylic alcohols and amines, which serve as important building blocks in the synthesis of a variety of natural products and pharmaceuticals.