received in U.K. for publication 8 Iiovember 1971) 11-Desoxyproetaglandlna are of considerable current interest as possible substrates for mlcrobiological hydroxylatlon at C(ll) (pro&mold numbering) and elsewhere, as poaslble antagonlsta of the prostagl&dlns in the E and F series, and as hypotenslve agents (1). We record here an especially simple and effective synthetic approach tc these substances. Blcyclo[4.2.O]oct-2-en-?-one (I) was prepared from 1,3-cyclohexadlene following a previously developed procedure for the conversion of cyclopentadiene to blcyclo[3.2. OJhept-a-en-B-one (2,3). The 1:l adduct from 1,3-cyclohexadiene and dlchloroketene (II) was obtained ln 78% yield by the simultaneous addition over 4 hr. of hexane solutions of dichloroacetyl chloride (2.1 equlv.) and trlethylamlne (2 equlv.) to 1,3-cyclohexadlene at 22-28' with a further 4-hr. reaction perlod at 26'. Dechlorination of II was effected by treatment with 5 equlv. of zinc ln acetic acid at 45-50' (1.5 hr.) followed by another equlv. of zinc at 70-75' (10 min.) to afford I as a colorless liquid, b. p. 85-90' (22 mm.), infrared max. 1775 cm. -1 (C=G) and 1640 cm. -' (C=C), ln 95% yield (4,5). Selective oxldatlon of I to the unsaturated Y-la&me III (4)