Synthesis and Diels-Alder reactivity of chiral 2-(alk-1-enyl)-1,3,2-diazaphospholidine 2-oxides

2-(Alk-1-enyl)-1,3,2-diazaphospholidine 2-oxides 4, containing the trans-N, N'-dibenzylcyclohexane-1,2-diamine chiral auxiliary, may be prepared by pal ladium(0)-mediated coupling of the phosphorous acid derivative 3 with alken yl halides. The X-ray crystal structure of the prop-1-enyl compound 4b has been determined. Some stereoselectivity has been observed in Diels-Alder re actions of the compounds 4. For example, the substituted (E)-acrylate ester 4c acts as a dienophile towards cyclopentadiene in hot toluene to give the four possible diastereoisomeric adducts in a 62:17:15:6 molar ratio; it ha s been shown that the structure of the main product 5c is consistent with a ttack of the diene on the less hindered face of the dienophile and that the methoxycarbonyl, rather than the diazaphospholidinyl group, has the endo- orientation. The dienyl-1,3,2-diazaphospholidine 2-oxide 4f acts as a diene in the reaction with 4-phenyl-1,2,4-triazoline-3,5-dione to give a 70:30 m ixture of adducts. (C) 1998 Elsevier Science Ltd. All rights reserved.