The mechanism investigation in substitution of 21-bromo-3alpha-hydroxyl-3beta-methoxymethyl-5alpha-pregnan-20-one with nucleophiles.

Abstract:

:A mechanistic study on the nucleophilic substitution of a strictly geometric 21-bromo-3alpha-hydroxyl-3beta-methoxymethyl-5alpha-pregnan-20-one was described. Reaction of the alpha-bromoketone with excess lithium imidazole followed by the addition of extra bases including n-butyllithium, methyllithium, lithium piperidine, and lithium pyrrolidine provided unexpected alpha-nucleophilic carbonyl adducts that derived from strong base. Data from HPLC and proton NMR suggested an epoxide as the intermediate. Two possible reaction pathways were proposed for the nucleophilic substitution reaction. One pathway is the normal SN2 substitution reaction, directly provided the imidazoly product without the formation of the unexpected alpha-substituted products. The other pathway went through an epoxide intermediate, in which imidazole anion or the strong bases added would attack from the less hindered site of the epoxide to give the substitution product.

journal_name

Steroids

journal_title

Steroids

authors

Chen CY,Wong FF,Lee YH,Chou SY,Huang JJ,Yeh MY

doi

10.1016/j.steroids.2006.07.004

subject

Has Abstract

pub_date

2006-11-01 00:00:00

pages

942-8

issue

11-12

eissn

0039-128X

issn

1878-5867

pii

S0039-128X(06)00158-9

journal_volume

71

pub_type

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