FACE-SELECTIVE DIELS-ALDER REACTIONS OF 3-FORMYL-6,6-DIMETHYLBICYCLO[3.1.1]HEPT-3-EN-2-ONE

The stereofacially differentiated enone aldehyde 11 was chosen to stud y the effects of steric and electronic influence on the Diels-Alder re action. Under Lewis acid catalysis, 11 adds to dienes at low temperatu res at a reasonable rate. Yields of desired chiral adducts are good to high with zinc chloride and boron trifluoride etherate catalysis. In all cases only products of addition to the Re face of general type 27 were observed. The regiochemistry of the adducts is exclusively that p redicted by the ortho and para rules. The stereochemistry shows a very high selectivity in favour of aldehyde-endo transition state products . Unusual byproducts were also obtained in some examples and mechanism s of these unexpected reactions are discussed.