Regio- and Enantioselective Synthesis of Trifluoromethyl-Substituted Homoallylic α-Tertiary NH2 -Amines by Reactions Facilitated by a Threonine-Based Boron-Containing Catalyst

A method for catalytic regio- and enantioselective synthesis of trifluoromethyl-substituted and aryl-, heteroaryl-, alkenyl-, and alkynyl-substituted homoallylic α-tertiary NH₂ -amines is introduced. Easy-to-synthesize and robust N-silyl ketimines are converted to NH-ketimines in situ, which then react with a Z-allyl boronate. Transformations are promoted by a readily accessible l-threonine-derived aminophenol-based boryl catalyst, affording the desired products in up to 91 % yield, >98:2 α:γ selectivity, >98:2 Z:E selectivity, and >99:1 enantiomeric ratio. A commercially available aminophenol may be used, and allyl boronates, which may contain an alkyl-, a chloro-, or a bromo-substituted Z-alkene, can either be purchased or prepared by catalytic stereoretentive cross-metathesis. What is more, Z-trisubstituted allyl boronates may be used. Various chemo-, regio-, and diastereoselective transformations of the α-tertiary homoallylic NH₂ -amine products highlight the utility of the approach; this includes diastereo- and regioselective epoxide formation/trichloroacetic acid cleavage to generate differentiated diol derivatives.

Enantioselective Iridium-Catalyzed Allylation of Acetylenic Ketones via 2-Propanol-Mediated Reductive Coupling of Allyl Acetate: C14-C23 of Pladienolide D

Highly enantioselective catalytic reductive coupling of allyl acetate with acetylenic ketones occurs in a chemoselective manner in the presence of aliphatic or aromatic ketones. This method was used to construct C14-C23 of pladienolide D in half the steps previously required.

γ-, Diastereo-, and Enantioselective Addition of MEMO-Substituted Allylboron Compounds to Aldimines Catalyzed by Organoboron-Ammonium Complexes

The first catalytic, broadly applicable, efficient, γ-, diastereo-, and enantioselective method for addition of O-substituted allyl-B(pin) compounds to phosphinoylimines (MEM=methoxyethoxymethyl, pin=pinacolato) is presented. The identity of the most effective catalyst and the optimal protecting group for the organoboron reagent were determined by consideration of the steric and electronic requirements at different stages of the catalytic cycle, namely, the generation of the chiral allylboronate, the subsequent 1,3-borotropic shift, and the addition step. Aryl-, heteroaryl-, alkenyl- and alkyl-substituted vicinal phosphinoylamido MEM-ethers were thus accessed in 57-92 % yield, 89:11 to >98:2 γ:α selectivity, 76:24-97:3 diastereomeric ratio, and 90:10-99:1 enantiomeric ratio. The method is scalable, and the phosphinoyl and MEM groups may be removed selectively or simultaneously. Utility is highlighted by enantioselective synthesis of an NK-1 receptor antagonist.

Electronically Activated Organoboron Catalysts for Enantioselective Propargyl Addition to Trifluoromethyl Ketones

A broadly applicable, practical, scalable, efficient and highly α- and enantioselective method for addition of a silyl-protected propargyl moiety to trifluoromethyl ketones has been developed. Reactions, promoted by 2.0 mol % of a catalyst that is derived in situ from a readily accessible aminophenol compound at ambient temperature, were complete after only 15 minutes at room temperature. The desired tertiary alcohols were isolated in up to 97 % yield and 98.5:1.5 enantiomeric ratio. Alkyl-, alkenyl-, alkynyl-, aryl- or heteroaryl-substituted trifluoromethyl ketones can be used. Utility is highlighted by application to a transformation that is relevant to enantioselective synthesis of BI 653048, a compound active against rheumatoid arthritis.

Highly Enantioselective Allylation of Ketones: An Efficient Approach to All Stereoisomers of Tertiary Homoallylic Alcohols

An optimized protecting group for allylboronates allowed the use of ketones in order to synthesize all isomers of quaternary homoallylic alcohols with high enantioselectivities. All symmetric isomers of the allylboronate were prepared in high yields and diastereoselectivities using S_n 2' reactions. The improved reactivity of the novel protecting group was verified by following the reaction kinetics with ¹ H NMR spectroscopy. Mechanistic studies using DFT calculations were conducted to investigate the new findings. Thus, the stereochemical outcome and enhanced reactivity can be rationalized.