Influence of diene substitution on Diels-Alder reactions between vinyl dihydronaphthalenes and (SS)-2-(p-tolylsulfinyl)-1,4-benzoquinone.

The asymmetric Diels-Alder reaction between 2-(E-2-acetoxyvinyl)-8-tert-butyl-3,4-dihydronaphthalene (8) and enantiopure (SS)-2-(p-tolylsulfinyl)-1,4-benzoquinone (1) takes place exclusively on the unsubstituted C(5)-C(6) double bond of (SS)-1 with a very high control of the chemo-, regio-, and diastereoselectivity of the process affording tetracyclic sulfinyl derivative 13a possessing five stereogenic centers. The analogue diene 9, lacking the tert-butyl group, gave a less chemoselective reaction (C(2)-C(3)/C(5)-C(6): 60/40) in favor of reaction through the sulfoxide-substituted double bond C(2)-C(3) of 1. Steric effects of the remote tert-butyl group and electronic factors due to the OAc substituent are controlling the process.