A new approach to cyclopentitols using CrCl2 mediated domino reaction and ring closing metathesis. The synthesis of 4a-carba-β-d-arabinofuranose and 4a-carba-β-d-lyxofuranose
作者:Girija Prasad Mishra、Batchu Venkateswara Rao
DOI:10.1016/j.tetasy.2011.04.012
日期:2011.4
described using Nozaki–Hiyama–Kishi conditions and ringclosingmetathesis. In this transformation ω-deoxy-ω-iodo ribofuranoside undergoes reductive elimination in the presence of CrCl2 to give the corresponding olefin-aldehyde, which was trapped by a nucleophile under the same conditions to afford the desired diolefinic species. The ringclosingmetathesis reaction on the diolefinic species with a Grubbs
All carbocyclic analogs of the pentofuranoses were synthesized starting from norborn-5-en-2-one (1). By using either base- or acid-catalyzed Baeyer-Villiger reaction of 1, the central intermediates 2 and 3 were obtained. The required functionalization of the olefinic double bond was achieved either by cis-hydroxylation in the case of the ribo, lyre, and alpha-xylo derivatives or by epoxidation and subsequent opening with aqueous perchloric acid. In the latter case, a pronounced selectivity for opening the epoxy alcohol in the 3-position was found. If an epoxy acetate with both functions on the same side of the ring was used, the epoxide was opened in the 2-position by neighboring group participation of the acetate. The requisite side chain degradation was accomplished either by conversion of the ester into an olefin and subsequent dihydroxylation/cleavage reaction or by Curtius rearrangement to the amine and its conversion into an acetate.