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From: ohad ilovich (ilovich$##$pob.huji.ac.il)
Date: Tue Mar 22 2005 - 08:59:15 EST


Hello there

i'm a first time user with a question concerning a mechanisem....

as you can see from the attached document the conformation of the C3 =
hydroxy can undergo flip-flop while undergoing benzilation.

if the reaction is done with NaH in dry THF the beta conformation is =
consereved.
if the reaction is done with NaH in dry toluene the flip flop occurs and =
we get the more stable alpha position. the Bz-Br is not needed for flip =
flop and it is enough to relfux with NaH for 3 hours to recieve a clean =
100% alpha product.
no double bond side product is formed that we can detect via NMR. when =
we tried to deuterate the C3 hydrogen and then reflux the steroid in NaH =
there was not hydrogen-deuterium exchange.

any ideas about a possible mechanisem?
any help would be appriciated

Ohad Ilovich


question.JPG

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