Highly Stereoselective Asymmetric Construction of an Acyclic Carbon Skeleton Having Two Adjacent Alkyl Substituents by Michael Addition of Optically Active Allenyltitaniums to Alkylidenemalonates
摘要:
[GRAPHICS]Enantio-enriched allenyltitaniums prepared in situ by the reaction of optically active secondary propargyl phosphates with a divalent titanium reagent Ti(O-i-Pr)(4)/2i-PrMgCl react readily with alkylidenemalonates with excellent regio- and diastereoselectivities to afford the Michael addition products with a high optical purity, thus opening up a new asymmetric method for construction of an acyclic carbon skeleton bearing two adjacent alkyl substituents.
A concise asymmetric synthesis of 5,8-disubstituted indolizidine alkaloids. Total synthesis of (−)-indolizidine 209B
作者:Yongcheng Song、Sentaro Okamoto、Fumie Sato
DOI:10.1016/s0040-4039(02)02149-4
日期:2002.11
A general access to 5,8-disubstituted indolizidinealkaloids has been developed, where the asymmetric addition of an optically active allenyltitanium to benzyl[4-(tert-butyldimethylsilyloxy)butylidene]amine (2) is the key reaction. As a typical example, (−)-indolizidine 209B was efficiently synthesized in 40% overall yield in a five-step reaction starting from readily available (S)-1-methyl-3-trim
Electrophilic amination of racemic and non-racemic allenyltitaniums. One-pot synthesis of α-hydrazinoalkynes from propargylic alcohol derivatives
作者:Duk Keun An、Koichiro Hirakawa、Sentaro Okamoto、Fumie Sato
DOI:10.1016/s0040-4039(99)00584-5
日期:1999.5
a reagent and dialkyl azodicarboxylates gave α-hydrazinoalkynes in good yields. The reaction, which proceeded with up to 86% chiral transfer, thus has opened up a newroute to opticallyactive α-hydrazinoalkynes from the opticallyactive propargylic compounds.