The commercial and research interest in 2 is obvious from
the many reports on its synthesis, mostly starting from 1. The
shortest reported synthesis requires only two steps: halogenation
of C-2, followed by a catalyzed substitution of the
halide with methoxide.6 However, the first step suffers poor
selectivity between C-2 and C-4, and the complete separation
of 2-halo- and 4-haloestradiols is very difficult to achieve.
A much more selective method involves the use of organoiridium
complex to direct the methoxylation process; thus,
2 was obtained from 1 in three steps with a good yield,
although a stoichiometric amount of iridium complex is
required.7 More recently, oxidation of 2-substituted estradiol
with peroxide has proven successful in the preparation
of 2 with high selectivity; however, five or more steps
were needed to convert 1 into 2.
8 We wish to report an
improved synthesis of 2 from 1 by directly introducing
a methoxy group onto C-2, using similar MOM-directed
C-2 lithiation chemistry followed by oxidation with cumyl
methyl peroxide.9