Structure of a SpiroeyeUe Chroman: 3',8-Bis(ehloromethoxy)- 4',5,6',7-tetramethylehroman-2- spiro- 1 '-eyelohexa-3',5 '-dien-2'-one

C20H22C1204, triclinic, PJ,, a = 10.241 (4), b = 9.067 (2), c = 11.206 (3)A, a= 105.57 (3), fl = 101.00 (4), y = 91.09 (3) °, Z = 2, F(000) = 416, g(Cu Ka) = 3.03 mm -1. Final R = 0.071 for 2681 observed reflections. Ring B is in a half-chair form whereas ring C is envelope. In the latter, there is indication of some conjugation; the two long and two short C-C bonds in the 1,3-diene moiety have mean values 1.451 (7) and 1.340 (6)/~ respectively. Introduction. The title compound (I), a spirocyclic chroman, has resulted from an unexpected reaction between 5-hydroxymethyl-2,4-dimethylspiroepoxy-2,4- cyclohexadienone and chlorotrimethylsilane (Cacioli, Mackay & Reiss, 1980). The reaction was carried out as a means of initiating possible ring-expansion, ring-opening and/or rearrangement processes, and forms part of an investigation of reactions of spiro- epoxycyclohexadienones with nucleophiles (Baldwin, Cacioli & Reiss, 1980).