Development of a General, Sequential, Ring-Closing Metathesis/Intramolecular Cross-Coupling Reaction for the Synthesis of Polyunsaturated Macrolactones
作者:Scott E. Denmark、Joseck M. Muhuhi
DOI:10.1021/ja1047363
日期:2010.8.25
macrocyclic lactones containing conjugated Z,Z-1,3-diene subunits is described. The centerpiece of the strategy is a sequential ring-closingmetathesis (RCM) that forms an unsaturated siloxane ring, followed by an intramolecular cross-coupling reaction with a pendant alkenyl iodide. A highly modular assembly of the various precursors allowed the preparation of unsaturated macrolactones containing 11-, 12-
Si-H insertion of a carbenoid, generated by decomposition of N2CHCO2Et, followed by a nucleophilic attack onto the Si-Cl bond by an alcohol. Alkylation of the title esters, reduction of the ester function and finally oxidation of the C-Si bond provide a facileentry to 1,2-diols.
scope of the Prins cyclisation, the higher stereoselectivesynthesis of multisubstituted tetrahydropyransfrom aldehydes and homoallylic alcohols, is expanded. A new approach for the stereoselectivesynthesis of polyketide precursors containing anti-1,3-diols, flanked by a variety of alkyl branches and functional groups is described. The approach is successfully exploited for the synthesis of (−)-sedamine
A variety of aldehydes undergo a tandem acetalization and intramolecular Prins cyclization with pent-4-ene-1,2-diol in the presence of 5 mol % scandium triflate and 15 mol % p-toluenesulfonic acid (TsOH) in dichloroethane at 80 °C to produce the corresponding bicyclic ethers, that is, 2,6-dioxabicyclo[3,2,1]octane derivatives in good yields and with high selectivity. The salient features of this methodology
An efficient synthesis of α-(alkoxysilyl)acetic esters by SiH insertion of carbenes, generated by rhodium catalyseddecomposition of diazoacetic esters, followed by nucleophilic displacement of Cl by ROH has been developed. Alkylation of these α-silyl carbonyls followed by Tamao oxidation of the CSi bond allow an easy access to terminal diols.