Substrate-Directed Diastereoselective Hydroformylation: Key Step for the Assembly of Polypropionate Subunits
作者:Bernhard Breit、Mario Dauber、Klaus Harms
DOI:10.1002/(sici)1521-3765(19991001)5:10<2819::aid-chem2819>3.0.co;2-z
日期:1999.10.1
Stereoselective hydroformylation of methallylic alcohols of types 3 and 4, that employed the substrate-bound catalyst-directing ortho-diphenyl-phosphanylbenzoyl (o-DPPB) group, was used as a key step for the construction of bifunctionalized stereotriads, which ale central building blocks of polyketide natural products. The required diastereomerically pure syn- and anti- starting methallylic alcohol systems 3 and 4 were obtained either by Cram-selective carbonyl reduction, Frater alkylation, or by chelation-controlled carbonyl reduction. Enantiomerically pure stereotriad building blocks were derived from a combination of an Evans aldol addition and subsequent o-DPPB-directed stereoselective hydroformylation (-->24). A crystal structure analysis for steretriad building block 24 confirmed the relative and absolute configuration of the stereogenic centers. Additionally, it provided evidence for a previously postulated preferred conformation of the catalyst-directing o-DPPB group as well as of the polyketide main chain.