9) 284-285 7.42-7.26 (IOH, m); 7.17-6.91 (14H, m); 4.18 (2H, s); 2.39 (4H. s); 1.84(2H, s) 308 (4.51), 314 (sh) 1720, 1700 1625 (10) 256-257 7.58 (2H, 1, J=2.5); 7.55-7.49 (4H, m); 7.44-7.34 (6H, m); 7.33-7.19 (6H, m); 314 (4.74), 320 (sh) 1690 1610 la1 7.09-7.03 (4H. m); 4.43 (2 H, s); 2.74-2.65 (4H, dAA'BB', J=2.5); 2.43-2.35 (4H. B B A A ) 2.47 (2H, m); 2.45-2.26 (2H. m); 1.65-1.36 (2H, m) (11) 156-157 7.53 (2H, t, J=2.5); 7.45-7.14 (20H, m); 4.62 (2H, 5); 2.81-2.67 (2H, m); 2.58-303 (4.66). 315 (sh), 1695 1625 la1 322 (sh)[a] Centrosymmetric stereoisomer of(l0) and f l l ) : M.p.=250.5-25ISoC; 6 e 7 . 3 4 (22H, m); 4.50 (2H, s); 3.1-2.6 (6H. m); 2.0-1.5 (2H, m) [6]. ~ [I] a) S. L. Buchwalter. G. t. Closs. J. Am. Chem. SOC. 97, 3857 (1975); b) G. [I] Review: M . Jones Jr.. R. A. Moss: Carbenes, Vol. I and 11, Wiley, New [2] P. P. Gaspar: Reactive Intermediates 1. 229 (1978). York 1973/75. ( I b ) , R = H