This paper is dedicated to Professor Peter Yates on the occasion of his 60th birthdayOTTORINO DE LUCCHI, VITTORIO LUCCHINI, MORENO ZAMAI, GIORGIO MODENA, and GIOVANNI VALLE. Can. J. Chem. 62, 2487 (1984).The cycloaddition of (E)-l,2-bis(benzenesulfonyl)ethylene (2) to 2-acetoxy-and 2-silyloxy-l,3-cyclodienes occurs in high yields and with high steroselectivity. Structure assignment has been based largely on 'H nrnr nuclear Overhauser effect (nOe) experiments on the isolated products. The cycloadducts 4a and 4b derived from the 2-oxa substituted cyclopentadienes have been further elaborated to the parent norbornenone, to the respective unsaturated sulfones 5 , and to the P-hydroxy substituted sulfone 6. The vinyl sulfones 5 have also been independently synthesized via cycloaddition of benzenesulfonyl acetylene. The sulfones obtained are potentially important starting molecules for the preparation of more complex targets.O-ITORINO DE LUCCHI, VIITORIO LUCCHINI, MORENO ZAMAI, GIORGIO MODENA et GIOVANNI VALLE. Can. J. Chem. 62, 2487(1984.La cycloaddition du (E)-bis(benz&nesulfonyl)-1,2-Cthylbne (2) sur les acCtoxy-2 et silyloxy-2 cyclodibnes-1,3 se produit avec des rendements ClevCs et avec une stCrCosClectivitC ClevCe. La dktermination des structures repose principalement sur des expCriences d'effet Overhauser nuclCaire (eon) et rmn du 'H qui ont Ct C rCalisCes sur les produits isolCs. De plus, une filiation a pu Ctre Ctabli entre les cycloadduits 4a et 4b, obtenus A partir des oxa-2 cyclopentadibnes, et la norbornCnone apparentke ainsi qu'avec la sulfone insaturie 5 et la P-hydroxysulfone 6. Faisant appel i une cycloaddition du benzbnesulfonylacCtylbne,

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