ture of 110flO"C for the signals of I-H, 7-H and 3-H, 5-H and thus an activation barrier of A Gf = 73 2 kJ/mol (Av = 409 Hz) for the degenerate Cope rearrangement (assuming that all of ( 7 a ) is present as the dication). The activation barrier is thus clearly larger than that of 3,4-homotropilidener8] but very similar to that of disubstituted 3,4-h0rnotropilidenes~~~. Received: June 14, 1977 [Z 759 IE] German version: Angew. Chem. 89, 668 (1977) CAS Registry numbers: (5a), 63466-72-8; ( 5 b), 63466-73-9; (6a),63466-74-0; [D,]-(6a),63466-77-3; 63466-84-2; ( 7 b), 63466-86-4; [D& 7 b), 63466-88-6; cis-1 ,2-cyclopropanediamine dihydrochloride, 63466-89-7; 2,4-pentanedione, 123-54-6; Na salt of malondialdehyde, 24382-01 -5 (66). 63466-78-4; [Da]-(6b), 63466-80-8; ( J u ) , 63466-82-0; [Ds]-(7~),
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