V. Bonnarme et al., Diels-Alder reaction of 4-bromo-6-spiroepoxycyclohexa-2,4-dienone with electron-rich and neutral dienophiles., TETRAHEDRON, 55(2), 1999, pp. 433-448
Spirodienone 1, prepared by Adler-Becker oxidation of 4-bromo-2-hydroxymeth
ylphenol undergoes [4+2] cycloaddition with various dienophiles (enol ether
s, enol esters, styrenes, N-methylvinylacetamide) under thermal conditions
(20-160 degrees C). Three sets of experiments have been carried out, either
with CH2Cl2 as solvent or neat with 1, or under tandem oxidation-cycloaddi
tion conditions with phase-transfer catalysis. Complete regio- and syn dias
tereofacial selectivities were obtained but a snitch in endo/exo selectivit
y has been observed between enol ethers and styrenes (endo addition), enol
esters (low selectivity) and an enamide (exo addition). The FMO analysis co
nfirms that theses reactions are under LUMOdiene control and that the obser
ved regioselectivity is in agreement with orbital coefficients. Except for
vinyl acetate, the formation of the major isomer is qualitatively confirmed
at the AMI level. (C) 1998 Elsevier Science Ltd. AII rights reserved.