Chemistry Reference
In-Depth Information
Fig. 8.16
Synthesis less
hindered silanediol 46 led to
the use of a difluorosilane
intermediate
69
of siloxane oligomers. It was this oligomerization difficulty that led to the develop-
ment of a useful variation in the hydrolysis procedure: following cleavage of the
aryl groups from silicon with triflic acid and ammonium hydroxide to hydrolyze
the (presumed) cyclized intermediate, the resulting crude mixture was then diluted
with 48 % HF. As anticipated, aqueous HF converted all of the silicon-heteroatom
bonds, including siloxanes, into the crystalline difluorosilane monomer
69
. Sus-
pending
69
in water and addition of sodium hydroxide led to a rapid dissolution and
clean formation of a water soluble, monomeric silanediol [
50
].
8.4.5
Angiotension-Converting Enzyme Inhibitors
Silanediol inhibitors of angiotensin-converting enzyme (ACE) were the most com-
plex synthesis challenges among the silanediols, and were also the first silanediol
inhibitors targeted. The first of the silanediol inhibitors,
70
and
71
, Fig.
8.17
, were
prepared with no control of stereochemistry [
66
]. Structure
70
was a mixture of
