Development of a Modified System to Provide Improved Diastereocontrol in the Linear-Selective Cu-Catalyzed Reductive Coupling of Ketones and Allenamides

Asymmetric Synthesis of Trisubstituted Vicinal Diols through Copper(I)-Catalyzed Diastereoselective and Enantioselective Allylation of Ketones with Siloxypropadienes

Chiral trisubstituted vicinal diols are a type of important organic compounds, serving as both common structure units in bioactive natural products and chiral auxiliaries in asymmetric synthesis. Herein, by using siloxypropadienes as the precursors of allyl copper(I) species, a copper(I)-catalyzed diastereoselective and enantioselective reductive allylation of ketones was achieved, providing both syn-diols and anti-diols in good to excellent enantioselectivity. DFT calculations show that cis-γ-siloxy-allyl copper species are generated favorably with either 1-TBSO-propadiene or 1-TIPSO-propadiene. Moreover, the steric difference of TBS group and TIPS group distinguishes the face selectivity of acetophenone, leading to syn-selectivity for 1-TBSO-propadiene and anti-selectivity for 1-TIPSO-propadiene. Easy transformations of the products were performed, demonstrating the synthetic utility of the present method. Moreover, one chiral diol prepared in the above transformations was used as a suitable organocatalyst for the catalytic asymmetric reductive self-coupling of aldimines generated in situ with B2(neo)2.

Development of regiodivergent asymmetric reductive coupling reactions of allenamides to access heteroatom-rich organic compounds

Organic compounds of biological importance often contain multiple stereogenic C-heteroatom functional groups (e.g. amines, alcohols, and ethers). As a result, synthetic methods to access such compounds in a reliable and stereoselective fashion are important. In this feature article, we present a strategy to enable the introduction of multiple C-heteroatom functional groups in a regiodivergent cross-coupling approach through the use of reductive coupling chemistry employing allenamides. Such processes allow for opportunities to access different heteroatom substitution patterns from the same starting materials.

Studies Toward Improved Enantiocontrol in the Asymmetric Cu-Catalyzed Reductive Coupling of Ketones and Allenamides: 1,2-Aminoalcohol Synthesis

Herein, we report the development of an improved system for the Cu-catalyzed enantioselective reductive coupling of ketones and allenamides through the optimization of the allenamide to avoid an on-cycle rearrangement. High enantioselectivities could be obtained for a variety of ketones. Use of the acyclic allenamides described herein selectively generated anti-diastereomers in contrast to cyclic allenamides that were previously shown to favor the syn-form. A rationale for this change in diastereoselectivity is also presented.