CHIRAL N-DIENYL-L-PYROGLUTAMIC ESTERS IN ASYMMETRIC HETERO-DIELS-ALDER REACTIONS WITH ACYLNITROSO DIENOPHILES

Abstract Asymmetric Diels-Alder reaction of the N-dienyl-L-pyroglutamic esters 1a-h with acyl nitroso dienophiles 4a-h gave diastereoisomeric adducts 6a-n, 7a-n with 12–90 % de , depending on solvents and temperature. An interpretation was gived. The “allylic effect” ( π C=C − σ ∗ N-C MO interactions) was found to be effective to account for the conformations of the adducts.