| Research Abstract |
Establishment of a synthetic method for chemoselectivity control in Diels-Alder reactions using two kinds of conjugate dienes, both of which can act as dienes and dienophiles depending upon the reaction conditions. Two possible combinations are possible for the chemoselectivity, and other selectivities such as regio- and diastereoselectivities. We have investigated the reactions using two different conjugate dienes, such as acyclic and cyclic ones, in the presence of a variety of catalysts.
2-Methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and cyclopentadiene have been selected as conjugate 1,3-dienes; nucleophiles such as the same 1,3-dienes and nitrones as 1,3-dipole have been used.. For the Diels-Alder reactions using these conjugate dienes and nitrone dipolar cycloadditions toward these conjugate dienes, a variety of Lewis acid catalysts such as halogens themselves, halonium ions having noncordinating halonium ions, N-haloammonium and N-halopyridinium salts have been applied in catalytic amounts. However, these catalysts are all ineffective for the activation.
Silyl cations, sulfonium cations, and selenium cations, which have been generated in situ by interaction of the corresponding halide derivatives with silver borontetrafluoride, have failed to accelerated the reactions. Allylic cation species have been generated from allylic acetates and carbonates in the presence of palladium zero catalysts and allowed to react with conjugate dienes and nitrones. However, no specific effect has not been observed.
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