Structure and molecular orbital study of ergoline derivatives. 1-(6-Methyl-8 beta-ergolinylmethyl)imidazolidine-2,4-dione (I) and 2-(10-methoxy-1,6-dimethyl-8 beta-ergolinyl)ethyl 3,5-dimethyl-1H-2-pyrrolecarboxylate toluene hemisolvate (II) and comparison with nicergoline (III).

(I): C19H22N4O2 (Registry No. 95688-34-9), m.p. greater than 573 K, Mr = 338.4, orthorhombic, P2(1)2(1)2(1), a = 8.392 (2), b = 13.004 (2), c = 15.676 (5) A, V = 1710.7 (7) A3, Z = 4, Dx = 1.31 Mg m-3, Mo Ka radiation, lambda = 0.71069 A, mu = 0.08 mm-1, F(000) = 720, T = 293 K, final R = 0.051 for 990 independent reflexions. (II): C26H33N3O3.1/2C7H8 (Registry No. 54370-23-9), m.p. 427-429 K, Mr = 481.64, monoclinic, P2(1), a = 11.595 (4), b = 14.274 (2), c = 16.103 (4) A, beta = 100.19 (3) degrees, V = 2623 (1) A3, Z = 4, Dx = 1.22 Mg m-3, Mo Ka radiation, lambda = 0.71069 A, mu = 0.07 mm-1, F(000) = 1036, T = 293 K, final R = 0.064 for 2738 independent reflexions. Two independent molecules constitute the asymmetric unit, together with a toluene molecule. Parallel investigations of the title compounds by single-crystal X-ray analysis and theoretical calculations have converged in showing an extended configuration of the side chain attached at the C8 atom of the ergoline nucleus.