The synthesis of PAF antagonist MK-287 is described. Our route utilizes a 5-aryl-substituted butyrolactone as the key optically active intermediate, which is constructed in four steps from commercially available 5-iodovanillin. Asymmetry is introduced using beta-chlorodiisopinocampheylborane to reduce a prochiral ketone. The second asymmetric center is installed relative to the existing stereocenter with stereocontrol exceeding 50:1. This step utilizes a copper-catalyzed Grignard displacement of an alpha-bromo ether. The alpha-bromo ether was generated using trimethylsilyl bromide activation of a silylated hemiacetal. The details leading to our development of the silyl acetal method for anomeric activation are also described.
A Practical, One-Pot Preparation of Diisopinocampheylchloroborane
作者:P. Simpson、D. Tschaen、T. R. Verhoeven
DOI:10.1080/00397919108021071
日期:1991.8
Abstract A one-pot preparation of the chiralreducingagentdiisopinocampheylchloroborane (Ipc2BCl) from α-pinene and borane methyl sulfide has been developed. The procedure obviates isolation of the air and moisture sensitive reagent, making it useful for large scale operations. Asymmetric reduction of ketones using the in situ prepared Ipc2BCl is comparable to that using isolated reagent.
The present invention is directed to in-situ preparation of diisopinocamphenyl chloroborane, and the use of same in the reduction of prochiral ketones to optically active alcohols such as those of formula B.
The compound of Formula B is useful in the production of 2,5-diaryltetrahydrofurans useful as PAF antagonists.