Ck. Mcclure et al., STRUCTURE DETERMINATION OF THE DIELS-ALDER PRODUCT OF A KETOVINYLPHOSPHONATE WITH E-1-ACETOXY-1,3-BUTADIENE, Tetrahedron letters, 37(13), 1996, pp. 2153-2156
The Diels-Alder reaction between diethyl ketovinylphosphonate 1 and E-
1-acetoxy-1,3-butadiene was performed with and without Lewis acid assi
stance to yield only one regio- and stereoisomer. Various 2-D NMR expe
riments confirmed that the acetyl group directed endo.