LIGHT-INDUCED CYCLOADDITIONS OF CAPTODATIVE ALKENES

Triplet excited 1-acylnaphthalenes add captodative alkenes, especially 2-amino-acrylonitriles, in a formal [4 + 2] mode to form 1,4-dihydro- 1,4-ethanonaphthalenes. This reaction is in some cases preceded by an independent and ultimately less efficient photoreversible 1,2-addition yielding cyclobutanaphthalene derivatives. There is no indication of a common intermediate partitioning into both types of products. Both a dditions occur with remarkable regio- and stereoselectivity. The chira lly labelled alkene S or R-2-(2-methoxymethyl-1-pyrrolidinyl)acrylonit rile is added in the [4 + 2] mode with over 99% diastereoselectivity l eading to practically enantiomerically pure 1,4-adducts. Sensitized cy clodimerizations of 2-morpholinoacrylonitrile are also discussed brief ly.