Chiral Unsymmetrically Substituted Bipyridine <i>N</i>,<i>N′</i>‐Dioxides as Catalysts for the Allylation of Aldehydes

Abstract

A series of unsymmetrically substituted diastereoisomeric ( R a ,R ) and ( S a ,R ) bipyridine N , N′ ‐dioxides was synthesized by using oxidative coupling of the corresponding metallated tetrahydroisoquinoline N ‐oxides in the presence of iodine. The N , N′ ‐dioxides contained substituted aryl groups with electron‐donating or electron‐accepting groups in the near vicinity of the N , N′ ‐dioxide moiety. Their catalytic activity was tested in a series of reactions of allyltrichlorosilane with various substituted benzaldehydes, thiophenecarbaldehyde, and cinnamaldehyde. The reactions proceeded with high enantioselectivities (up to 98 % ee ) with catalyst loadings as low as 0.5 mol‐%. Furthermore, allylation reactions of ( E )‐3‐iodomethacrylaldehyde were also carried out to give chiral ( E )‐1‐iodo‐2‐methylpenta‐1,4‐dien‐3‐ol, a convenient building block for the synthesis of natural products. The allylations proceeded with high enantioselectivities (up to ca. 99 % ee ) with a catalyst loading of 2.5 mol‐%.