[2-PHOTOADDITION OF 2-AMINOPROPENENITRILES TO DIARYLETHANEDIONES - A PRODUCT STUDY(2])

A selection of symmetrical (1a-f and unsymmetrical (4a.b) diarylethane diones, starting from their (3)(n, pi) states, undergoes smooth head- to-head [2 + 2] photoaddition of various 2-aminopropenenitriles 2A-F t o form oxetanes 3, 5 and 6 in moderate to good yields. Only one diaste reomer out of two a-priori possible regioisomers is formed in each cas e. The connectivity and the preferred geometry of the products is rati onalized in terms of the geometry of the most easily accessible and mo st stabilized (including captodative stabilization) 1,4-biradical inte rmediate. Whereas 2-naphthyl-substituted diones 1f and 4b form oxetane s, 1,1'-naphthil and 1-(1-naphthyl)-2-phenylethanedione are ineffectiv e.