Diastereoselective silacyclopropanations of functionalized chiral alkenes.
Lithium reduction of di-tert-butyldichlorosilane and thermal silylene transfer (105-125 degrees C) are complementary methods for the highly diastereoselective silacyclopropanations of a range of functionalized chiral olefins to afford complex silacycles. We have shown that functionalized cyclohexenes, cyclopentenes, norbornenes, and 1,1-disubstituted alkenes undergo silacyclopropanation with excellent diastereoselectivity (92:8 to >99:1). Our results demonstrate that steric interactions, rather than oxygen-directing effects, control the approach of the silylene or silylenoid intermediate to the olefin. We believe that the sterically demanding nature of the di-tert-butylsilylene species prevents coordination to the oxygen functionality. Thermal silylene transfer conditions exhibit broad functional group tolerance; the elevated temperatures for silylene transfer, however, cannot be employed for the silacyclopropanation of substituted cyclohexenes and 1,1-disubstituted alkenes. Elaboration of the resulting functionalized silacyclopropanes provides an efficient route to polyoxygenated products.
Driver
Tom G
TG
Department of Chemistry, University of California, Irvine, California 92697-2025, USA.
Franz
Annaliese K
AK
Woerpel
K A
KA
D000475:Alkenes / Q000737:chemistry*; D003521:Cyclopropanes / Q000737:chemistry*; D006844:Hydrocarbons, Cyclic / Q000737:chemistry; D012821:Silanes / Q000138:chemical synthesis / Q000737:chemistry*; D013237:Stereoisomerism
D000475:Alkenes; D003521:Cyclopropanes; D006844:Hydrocarbons, Cyclic; D012821:Silanes