Chiral tricarbonyl(h6-arene)chromium(0) complexes in stereoselective hetero Diels-Alder reactions

Zinc chloride-promoted stereoselective cyclocondensation of the Danishefsky diene [E-MeOCH:CHC(:CH2)OSiMe3] to ortho-substituted benzaldehyde and benzaldimine chromium tricarbonyl complexes gave 2,3-dihydro-4-pyridinone and 2,3-dihydro-4-pyranone derivs. in fairly good (75-90%) yields and with complete stereoselection. Exposure of CH2Cl2 solns. of the latter to sunlight gave the corresponding uncomplexed 2,3-dihydro-4-pyridinone and 2,3-dihydro-4-pyranone derivs.