Stereoselective synthesis of an analog of podophyllotoxin by an intramolecular Diels-Alder reaction

…, PYS Lam, MM Mansuri, LM Speltz

Index: Jung, Michael E.; Lam, Patrick Yuk-Sun; Mansuri, Muzzamil M.; Speltz, Laurine M. Journal of Organic Chemistry, 1985 , vol. 50, # 7 p. 1087 - 1105

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Citation Number: 83

Abstract

The dihydrobenzocyclobutene 90 having a 4-hydroxycrotonate unit attached via an ester linkage as an internal dienophile can be cyclized to a 3: l mixture of the trans lactone 92 (an analogue of podophyllotoxin, 1) and the cis lactone 93. This stereoselective reaction proceeds via the intermediacy of the o-quinodimethane 91 which cyclizes from the endo transition state 91n in preference to the exo-one 91x, presumably because of stabilization ...