Reagent-controlled enantioselective homoaldol reaction with chiral 1-oxyallyllithium derivatives. Enantio-divergent tuning by achiral titanium reagents
作者:Thomas Krämer、Dieter Hoppe
DOI:10.1016/s0040-4039(00)95614-4
日期:——
carbamates are deprotonated by n-butyllithium with retention of configuration. Lithium titanium exchange by Ti(OPr)4 proceeds with retention and by ClTi(NEt2)3 with inversion of configuration. The stereochemical course of addition to aldehydes is mainly determined by the chiral center of the metal allyl reagents to offer a flexible route to both enantiomers of highly substituted ketones.
Enantiomerically enriched allystannanes from chiral allyllithium derivatives and their highly regio-, diastereo- and enantioselective hydroxyalkylation
作者:Thomas Krämer、Jan-Robert Schwark、Dieter Hoppe
DOI:10.1016/s0040-4039(01)93417-3
日期:——
Enantiomerically enriched 1-(N,N-diisopropylcarbamoyloxy)-1,3-dimethylallyllithium: stereochemistry of the stannylation, titanation, and the homoaldol reaction
Contrarely to our former assumption1,3, the title compounds 3 and 9 [(2E)- and (2Z)-isomer, (-)-sparteine or TMEDA complex] are substituted by means of trialkyltin halides in an anti-S(E)' process. The optically active allylstannanes, thus produced, and aldehydes undergo a stereospecific homoaldol reaction under the influence of TiCl4 which involves a second anti-S(E)' transmetallation.