An efficient protocol for Sharpless-style racemic dihydroxylation

Abstract

An Efficient Protocol for Sharpless-Style Racemic Dihydroxylation.-Racemic dihydroxylation of various alkenes is efficiently achieved under conditions similar to those of Sharpless asymmetric dihydroxylation using OsCl 3 -quinuclidine as catalytic system and methanesulfonamide as a further additive. Scope and limitation of the reaction are studied, and diastereoselectivity in the dihydroxylation of compounds with stereogenic centers, e.g. (VII) and (IX), is found to be only moderate.

A new synthesis of the F5 furan fatty acid and a first synthesis of the F6 furan fatty acid

“…The (E)-iodoalkene 6 was prepared in excellent yield from 1-heptyne by sequential hydroalumination using Dibal-H and halogenation by N-iodosuccinimide 17 ; a subsequent Sonogashira coupling 18 with iodo-ester 5b then gave the (E)-enyne 7. As we clearly did not require homochiral material, this was then bis-hydroxylated regioselectively at the alkene function, as originally reported by the Sharpless group, 19 but using the simpler achiral Warren procedure, 20 which delivered an excellent 86% yield of the required alkyne-diol 8. We were dismayed to find that our initial attempts to carry out a 5-endo-dig iodocyclisation 12 using the alkene-diol 8 met with almost complete failure.…”

Reaction of 1,1′‐Divinyl Ferrocene with One‐Electron Oxidants: Entry into Functionalised [4]Ferrocenophanes and Observation of an Isotope‐Dependent Chemoselectivity Effect

“…During reaction optimisation studies, it was found that the efficiency of the oxidative cyclisation of 2 to 4 is sensitive to the reagents and reaction conditions; thus, exposure of 2 to other dihydroxylation reaction conditions led to reduced yields of 4 and other products. For example, employing Warrens racemic dihydroxylation reaction conditions [14] gave keto-alcohol 4 in 57 % yield, along with d/l-diol d/l-6 in 15 % yield (Scheme 4). The structure of this diol byproduct was verified by comparison with NMR data obtained for the mixture of meso-and d/l-diol products obtained from the reduction of keto-alcohol 4 (vide infra).…”

Expedient Syntheses of β‐Iodofurans by 5‐endo‐dig Cyclisations

“…[11] The enynes were obtained in turn from Sonogashira couplings of a 1-alkyne and a 1-bromoalkene, all of which are commercially available. Success in the key cyclisation step (Scheme 5) turned out to be readily achieved using conditions employed previously in our 5-endo-trig cyclisations.…”