Elsevier

Tetrahedron

Volume 22, Issue 3, 1966, Pages 949-954
Tetrahedron

Synthesis of Δ7-1-methylbicyclo[5,4,0]undecene-2,9-dione and its condensation with acetylene

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Abstract

Michael addition of methylvinyl ketone to 2-methylcycloheptane-1,3-dione (II) obtained by methylation of cycloheptane-1,3-dione furnishes 2-methyl-2(3′-oxobutyl) cycloheptane-1,3-dione (III) which is cyclized and dehydrated in a single step to afford the title compound (Ic) in the presence of a mixture of pyrrolidine and acetic acid. A by-product isolated in this cyclization is the bridged ketol VII. Treatment of III with p-toluenesulphonic acid gives predominantly the acid IV and only low yields of Ic. The reaction of Ic with lithium acetylide furnishes an unexpected product formulated as IX. An explanation for the differing course of ethynylation of the analogous diones Ia, Ib and Ic is given.

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