Chemo-, Regio-, Diastereo-, and Enantioselective Palladium Allylic Alkylation of 1,3-Dioxaboroles as Synthetic Equivalents of α-Hydroxyketones

We describe the development of a Pd-catalyzed asymmetric allylic alkylation (Pd-AAA) of acyclic α-hydroxyketones using boronic acids as traceless templates. Condensation of boronic acids with hydroxyketones generates 1,3-dioxaboroles, which can be used directly as pronucleophiles in Pd-AAA reactions. This strategy enables control of the enolate geometry, while removing the issue of O-alkylation. Allylic alcohols can be directly ionized in the presence of Pd(0) and chiral ligands to afford alkylation products with regio- and enantioselectivity. Additionally, a dynamic kinetic asymmetric transformation of allenyl electrophiles affords C-alkylation products in high regio-, diastereo-, and enantioselectivity. To the best of our knowledge, this method represents the first example in Pd-AAA for setting point chirality on a nucleophile simultaneous to stereoinduction on an axial chiral allene.

15 beta-hydroxysteroids (Part III). Steroids of the human perinatal period: the synthesis of 3 beta, 15 beta, 17 alpha-trihydroxy-5-pregnen-20-one. Application of n-butyl boronic acid protection of a 17,20-glycol

We report the synthesis of 3 beta,15 beta,17 alpha-trihydroxy-5-pregnen-20- one (1) from 3 beta,15 beta-dihydroxy-5,16-pregnadien-20-one (11) in 7 steps using boronate derivatives as a means of protecting the 17,20-glycol side-chain of steroid intermediates. 16 alpha,17 alpha-Epoxy-3 beta,15 beta-dihydroxy-5- pregnen-20-one (12), an intermediate in the synthesis was prepared by epoxidation of 11 using a mixture of sodium hydroxide and hydrogen peroxide. Reduction of 12 with lithium aluminium hydride gave the two isomers of 5-pregnene-3 beta, 15 beta,17 alpha,20 (S+R)-tetrol (13a and 13b) which on subsequent reaction with n-butyl boronic acid gave 5-pregnene-3 beta,15 beta,17 alpha, 20(S+R)-tetrol 17 alpha,20-butyl boronate (15a and 15b). Acetylation with acetic anhydride and pyridine yielded 3 beta,15 beta-diacetoxy-5-pregnene-17 alpha,20(S+R)-diol 17 alpha,20(S+R)-butyl boronate (15c and 15d). Oxidative cleavage of the boronic ester using sodium hydroxide and hydrogen peroxide gave 3 beta,15 beta-diacetoxy-5-pregnene-17 alpha,20(S+R)-diol (13c and 13d). After isolation of these latter two products, dibromide protection of the C-5,6 olefin of 13d and oxidation with N-bromosuccinimide gave 3 beta,15 beta-diacetoxy-17 alpha-hydroxy-5-pregnen-20-one (16) which on deacetylation gave in good yield (35%) the desired product 3 beta,15 beta,17 alpha-trihydroxy-5-pregnen-20-one (1) in an overall yield of 24% from 11.