Aromatic Spiranes, XXIII [1]: Synthesis of Unsymmetrically Substituted Dimethyl-2,2′-Spirobiindan-1,1′-dionen

Article abstract of DOI:10.1007/BF00810885

Both spirodiketones 7 and 8 were obtained as a mixture (56:44) by treatment of dicarbonic acid 5 with polyphosphoric acid (PPA). 5 was accessible from dimethylester 3, synthesized by retro-Claisen reaction between 1 and 2. In the same way, 30 was obtained via 27. The preparation of the pure spiro compounds 7 and 8, resp., was achieved by aldol reaction between 9 and 10 or 9 and 16, resp. Short treatment of the resulting compounds 11 and 17 with diazomethane yielded the methylbenzoates 12 and 18. Prolonged reaction (several hours) gave the pyrazole compounds 14 and 19, resp., which were also obtained (several days) from phthalides 14 and 20. The latter were formed from the benzylidene compounds 11 and 17, resp., by heating. 11 and 17 (after hydrogenation to 15a and 21a) were cyclized either with PPA or thermically to the spiro compounds 7 and 8. The main product 20 was cyclized thermically to 8 after reduction with zinc to a mixture of 21a and 8 (20:75).