Face Selectivity of the Diels‐Alder Additions of Exocyclic Dienes Grafted onto 7‐Oxabicyclo[2.2.1]heptanes

Stereoselective syntheses of 2exo, 3exo‐bis (chloromethyl)‐5‐[(Z)‐chloromethylidene]‐ (9), 2exo, 3exo‐bis (chloromethyl)5‐[(E)‐chloromethylidene]‐ (10) and 2exo, 3exo‐bis(chloromethyl)‐5‐[(E)‐methoxymethylidene]‐6‐niethylidene‐7‐oxa‐bicyclo[2.2.1]heptane (13) are presented. Double elimination of HCI from 9, 10 and 13 yielded 2‐[(Z)‐chloromethylidene]‐ (14), 2‐[(E)chloromethylidene]‐ (15) and 2‐[(E)‐methoxymethylidene]‐3,5,6‐mmethylidene‐7‐oxabicycio[2.2.1]heptane (18), respectively, without loss of the olefin configuration. Ethylene tetracarbonitrile (TCE) and N‐phenyltriazolinedione (NPTAD) added to these new exocyclic dienes and tetraenes preferentially onto their exo‐face. The same face selectivity was observed for the cycloadditions of TCE to the (Z)‐ and (E)‐chlorodienes 9 and 10, thus realizing a case where the kinetic stereoselectivity of the additions is proven not to be governed by the stability of the adducts. The exo‐face selectivity of the Diels‐Alder additions of dienes grafted onto 7‐oxabicyclo [2,2.1]heptanes contrasts with the endo‐face selectivity reported for a large number of cycloadditions of dienes grafted onto bicyclo[2.2.1]heptane skeletons.