Stereocontrol of three contiguous chiral centers of brassinosteroid side chain by using .alpha.-alkoxy organoleads
摘要:
The reaction of steroidal aldehyde 2 with chiral alpha-methoxyorganolead (S)-3 in the presence of TiCl4 gave the Cram-syn product 4, a precursor of 28-norbrassinolide, in 90% yield as a single stereoisomer. A kinetic resolution was observed in the TiCl4 mediated reaction of 2 with (+/-)-3; again 4 was produced in 99% yield as a single isomer.
Synthesis of α-alkoxyalkyltributyllead compounds via the reaction of tributylplumbyllithium with α-chloroethers, and the conjugate addition of tributylplumbyllithium to enones
摘要:
Alpha-alkoxyalkyltributylleads 1 were prepared from the reaction of tributylplumbyllithium with alpha-chloroethers 2. This procedure is more convenient than the conventional method which involves transmetallation from the corresponding alpha-alkoxyalkyltrialkyltin. Tributylplumbyllithium was also used for the synthesis of beta-oxo-organo-lead 4.