Regioselectivity of the Reactions of Heteroatom-Stabilized Allyl ...

Scheme 35
Scheme 36
Treatment of monolithioallyl phenyl sulfone 198
with an excess of n BuLi affords a mixture of 1,1dilithiated
allyl phenyl sulfone 199 and 1,o-dilithiated
200 124 as shown by quenching with an excess of
benzaldehyde to give the 1,o-201 and 3,o-(E)-diadducts
202 and the 1,3-(E)-diadduct 197 (Scheme
35). 125 With alkyl halides, double alkylation of the
dianion mixture occurs selectively at the R-position
to form 196 126 and this is used in the synthesis of
pheromone analogues. At 50 °C, the R,o-dianion 200
is converted into the thermodymically more stable
R,R-dilithio intermediate 199. 124
Predominantly R-products are also found for the
electrophilic reactions of the dianion of N-phenyl-2-
[(phenylsulfonyl)methyl]propenamide 204, which is
used for the preparation of R-methylene-�-lactams
209, 127 the synthesis of R,�-unsaturated amides 208
and 5,6-dihydro-2H-pyrans 210 (Scheme 36). 128
Scheme 37
Scheme 38
677
The allyl sulfone dianion 212 gives regiospecific
and stereoselective reactions with alkyl bromides,
aldehydes and electrophilic olefins at the R-position
to the sulfone group to form 213 (Scheme 37). 129
Furthermore, for the dienolate anion 215, derived
from the γ-(phenylsulfonyl)crotonate 214, R-alkylation
is predominantly observed to give 216 (Scheme
37). 130 The complementary conjugative effects of the
sulfonyl and the carbonyl substituents result in
preferential formation of 216. Catura and Najera
reported that the treatment of methyl (E)-4-tosyl-2butenoate
of type 214 with 2 equiv of sodium hydride
and different mono- and dihalides gives mixtures of
γ,γ- and R,R- orR,γ- and γ,γ-dialkylated products. 131
Similarly to allyl sulfones, deprotonated 2,5-dihydrothiophene
1,1-dioxide 217 reacts with alkyl halides,
aldehydes to give exclusively R-products 218.
Subsequent desulfonylation (thermolysis) leads to
substituted buta-1,3-dienes 219. 132-134 Tso et al. have
prepared 2,2-dialkylated or spiro analogues 221 or