Abstn&--A l?riedel-&& condensation of l,?-~~ox~aph~~e with the anhydride IV gave a mixture of products from which, after ester&&on, the ketoestem IX and X could be isolated in 16 and 4.25 % yield, respectively. These were hydrogenolysed with Pd-C to the desoxyesten XI and XII. Cyclodehydration of the latter with an a&o-hydrochloric acid mixture furnished the desired estrahexaene III. Reaction of the lithio derivative of 2-methoxynaphthalene with the dimethyl ester Vc yielded the hydroxyester XVb which was dehydrated to the unsaturated compound XVIII. Assi-nt of structures to the isomers IX and X by means of mass spectrometry is discussed. REACTION of the 7-carbon &methyltricarbahyIic acid anhydride (I) with 1,7dimethoxynaphthalene was reported to render the tricyclic intermediate II, which was then converted1 into the estrahexaene derivative III, utilizing the methyl acrylate reaction developed by Wilds and collaborators .s The latter Michael-type reaction serves, in effect, to introduce the carbon atoms 15 and 16 stilI missing in II.
We have now devised another method of synthesis of HI by attaching a g-carbon fragment comprising atoms 11, 12, 13, 14, 15, 16, 17, I8 and 20 of rings C and D to 1,7dimethoxynaphthalene (Chart I). This fragment contains all the carbon atoms present in the anhydride I, plus the two carbon atoms derived from the acrylate reaction. The compound in question is 2-me~yl-2(~~x~e~y~)-3ox~cl~ pentanecarboxyhc acid anhydride (IV). A synthesis of the diethyl ester Vb, corresponding to this anhydride, has been describedS and involves condensation of ethyl acetoacetate with ethyl cyanoacetate, addition of hydrocyanic acid and cyanoethylation of the resulting dicyanoester VI (an intermediate in the synthesis of &methyltricarballylic acid4). Hydrolysis and esterifkation furnished the tetramethyl ester VII which, on Die&mann cyclization, yielded the @-ketoester VIII. Hy~olys~ of WI, decarboxyiation and esterification furnished the ester Vb. Presently we have isolated the free acid Va and dehydrated it with acetic anhydride to the anhydride IV.