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

Scheme 25
Scheme 26
γ-attack in the reaction with benzaldehyde to give
152 alongside a minor amount of 153 from R-attack.
Carbonyl attack is possibly thermodynamically controlled
while the alkylation is under kinetic control.
Chiral allylic sulfoxide 154 gives regiospecific
asymmetric conjugate addition to various cyclic enones
(cf. 155) with high diastereomeric excess 100 via a 10membered
“trans-decalyl” or “trans-fused chairchair”
transition structure 156 furnishing 1,4-γadducts
158 (Scheme 26). 92,101-106 Better regio- and
diastereoselective addition is achieved by the utilization
of sterically demanding auxiliary-modified allylic
sulfoxides 157 107 for which the relative configuration
depends on whether the product is formed under
kinetic or thermodynamic control. 108
In comparison to cyclic enones, sulfoxides add to
acyclic enones via a six-membered transition intermediate
160, 161, 164, and 165 which is characteristic
for the reaction of unsaturated carbonyl derivatives
159 with allyl compounds 163 (M ) B, Ti, Li,
etc.) to give 162 and 166 (Scheme 27). 109 If large
substituents on the acyclic enone increase its steric
rigidity the reaction is predicted to proceed via the
extended trans-decalyl transition structure (see
Scheme 26). 110
4. Allyl Sulfones (CdC−C−SO2R)
Allyl sulfone anions 167 are obtained by treatment
of the corresponding sulfur compound with n BuLi in
THF, or RMgX, or in a two-phase system of concentrated
aqueous NaOH and a quaternary ammonium
catalyst. Lithiated allyl sulfone reacts R with alkyl
halides or Me3SiCH2Cl give 170 111-113 and with
Scheme 27
Scheme 28
675
aldehydes to give R-adducts 168 regio- and diastereoselectively
(Scheme 28). 114
R-(Hydroxymethyl)allyl sulfones 172 are obtained
upon hydroxymethylation with paraformaldehyde (Rattack)
and the products can be converted into
2-substituted 1,3-butadienes 173 (Scheme 28). 115 The
reaction of allyl phenyl sulfone with a chiral epoxide
(cf. 169) is used in the synthesis of constanolactone
E (Scheme 28). 116
Similarly, the R-product 176 is obtained from the
alkylation of prenyl sulfone 174. 117 This is used for
the synthesis of cyclized products (cf. 177) by addition
of AlCl3 (Scheme 29).
Furthermore, allyl sulfones 178 can be converted
to vinyl sulfones 180 via silylation at the R-carbon