, 78 (1949)). Ia: mp. 165–167°C; UV(EtOH) (ε) 266 (1.2 x 10 4 ) and 347 nm (7.3 x 10 3 ). Ib: mp. 159–161°C; UV(EtOH) (ε) 264 (1.1 x 10 4 ) and 345 nm (6.4 x 10 3 ); IR (KBr) 1650 cm −1 ; δ(CDCl 3 ) 1.15 (t, 3H), 3.90 (q, 2H), 7.1–7.6 (m, 10H), and 8.33 (s, 1H). Satisfactory elemental analyses have been obtained for all new compounds. ... We could not detect the corresponding intramolecular [2+2] cyclization product when 2-pyrazinone (Ia and b) was irradiated in a ...