Preparation of γ-trimethylsilylallyldibutylstannane grafted on solid support: a clean and easily recyclable reagent for the synthesis of 2,6-disubstituted dihydropyrans
annane grafted on an insoluble macroporous polymer is reported. This bimetallic reagent was treated with aldehydes in the presence of indium trichloride to afford in good yields both symmetrical and unsymmetrical cis-2,6-disubstituted dihydropyrans, practically uncontaminated with organotin residues (less than 20 ppm). The potential for regeneration and reuse of this supported bimetallic reagent is
Bi(OTf)<sub>3</sub>-, TfOH-, and TMSOTf-Mediated, One-Pot Epoxide Rearrangement, Addition, and Intramolecular Silyl-Modified Sakurai (ISMS) Cascade toward Dihydropyrans: Comparison of Catalysts and Role of Bi(OTf)<sub>3</sub>
作者:R. Frederick Lambert、Robert J. Hinkle、Stephen E. Ammann、Yajing Lian、Jia Liu、Shane E. Lewis、Robert D. Pike
DOI:10.1021/jo201478d
日期:2011.11.18
Catalytic quantities of bismuth(III) triflate efficiently initiate the rearrangement of epoxides to aldehydes, which subsequently react with (Z)-delta-hydroxyalkenylsilanes to afford 2,6-disubstituted 3,6-dihydro-2H-pyrans. Isolated yields of desired products using Bi(OTf)(3) were compared with yields obtained when the reactions were run with TfOH and TMSOTf in the presence and absence of several additives. These studies, as well as NMR spectroscopic analyses, indicate an initial Lewis acid/base interaction between Bi(OTf)(3) and substrates providing TfOH in situ.
Highly Stereoselective Prins Cyclization of (<i>Z</i>)- and (<i>E</i>)-γ-Brominated Homoallylic Alcohols to 2,4,5,6-Tetrasubstituted Tetrahydropyrans
作者:Feng Liu、Teck-Peng Loh
DOI:10.1021/ol070506n
日期:2007.5.1
An efficient method has been developed to construct 2,6-cis-4,5-dibromo-tetrasubstituted tetrahydropyran ( THP) rings with well-controlled stereochemistry in moderate to high yields.