19c a Overall isolated yields of purified products, based on cyclobutenone or acyl chloride. See ref 12. One-step annulations. For 12: CHCl,, 137 OC, 2 h. For 13: cyclohexane, 100" C, 41 h. The intermediate divinylcyclobutnnone (s) were isoldted and purified prior to Cope rearrangement. For 9-11, see text. For 12:[2 t 21 cycloaddition (CHCl,, 73" C, 19 h) gave 12 (16%)+ 21 (34%); further therniolysis of 21 was then effected in toluene (150" C, 45 min). ...