Page 866 - Advanced Organic Chemistry Part B - Reactions & Synthesis

842 OMOM OH
CH O InCl 3
CHAPTER 9 + CH 3 SnBu 3 CH 3
Carbon-Carbon OMOM
Bond-Forming Reactions
of Compounds of Boron,
Silicon, and Tin These reactions are believed to proceed via transmetallation. Configurational inversion
occurs at both the transmetallation and addition steps, leading to overall retention of
the allylic stereochemistry.

H OMOM
SnBu InCl H R
3 2
InCl 3 RCH O O S R
Cl OMOM
CH OMOM In R
CH 3 OMOM 3 CH 3
S Cl CH OH
R 3
These reagents are useful in enantioselective synthesis and are discussed further in the
following section.
9.3.2.4. -Oxygen-Substituted Stannanes. Oxygenated allylic stannanes have been
synthesized and used advantageously in several types of syntheses. Both - and -
alkoxy and silyloxy stannane can be prepared by several complementary methods. 177
E- -Alkoxy and silyloxy allylic stannanes react with aldehydes to give primarily syn
adducts. 178

OH
CH 3 OTBDMS O CH BF 3 CH 3
+
SnBu 3 TBDMSO

79% yield, 98:2 syn

Allylic silanes with -alkoxy substituents also give a preference for the syn stereo-
chemistry. 179

OH
OH
BF 3
RCH O + SnBu 3 R + R
OCH 3 –78 °C
OCH 3 OCH 3
anti
syn
R syn:anti
Ph 10:1
i-Pr 25:1
c-C H 5:1
6 11
Improved stereoselectivity is observed with methoxymethoxy (MOM) and TBDMSO
substituents. 180

177
J. A. Marshall, Chem. Rev., 96, 31 (1996).
178
J. A. Marshall, J. A. Jablonowski, and L. M. Elliott, J. Org. Chem., 60, 2662 (1995).
179 M. Koreeda and Y. Tanaka, Tetrahedron Lett., 28, 143 (1987).
180
J. A. Marshall and J. A. Welmaker, J. Org. Chem., 57, 7158 (1992).