Diels-Alder dimerization of a hexenylidene-substituted Benzofuran-2(3H)-one

Abstract

(Z)-7-t-Butyl-5 methoxy-3-[(Z)-2?-methoxy-5,5'-dimethyl-4'-oxohex-2'-enylidene]benzofuran-2(3H)-one has been found to undergo Diels-Alder dimerization in which the exocyclic double bond adds to the s-cis diene moiety. The stereochemistry of the Diels-Alder dimer was established by a single-crystal X-ray structure determination. Crystals of the dimer, C₄₄H₅₆O₁₀, are monoclinic, P2₁/n, a 12.23(1), b 19.43(2), c 18.71(2) Å, β 107.76(7)º, Z 4; a residual of 0.046 was obtained for the 2519 'observed' reflections. In the dimer, two benzofuranone moieties are situated so as to be vicinal spiro substituents of the cyclohexene formed in the Diels-Alder addition. The bond between the two benzofuranone units is unusually long [1.597(6)Å]. The shielding of one aromatic hydrogen in the n.m.r. spectrum of the dimer results from the disposition of the two aromatic systems.