Reaction of 2,6-disubstituted phenols with vinyllead triacetates and alk-1-ynyllead triacetates: Synthesis of 6-vinyl- and 6-alkynyl-cyclohexa-2,4-dienones and crystal structure of 1,3,5,7-tetramethyl-3,5-bis(phenylethynyl)-1,3,4,4a,5,8a-hexahydro-1,4- ethenonaphthalene-2,6-dione

(E)-Styryllead triacetate 9, generated by reaction of lead tetraacetate with trimethyl[(E)-styryl]-stannane 7, has been found to react with 2,4,6-trimethylphenol 1 to give the 6-(E)-styrylcyclohexa-2,4-dienone 11 in high yield. This electrophilic vinylation reaction has been investigated for the vinyllead triacetates 9 and 10 and the 2,6-dimethylphenols 1, 13, 14 and 15. An analogous alkynylation reaction occurred when phenylethynyllead triacetate 24 was treated with 2,4,6-trimethylphenol; however, the product in this case, cyclohexadienone 25, underwent a Diels-Alder dimerisation to give the 1,4-ethenonaphthalene 26. The product 28 from a reaction of the phenylacetylenelead compound 24 and 2,6-dimethylphenol behaved similarly, and here the 1,4-ethenonaphthalene structure 27 for the dimer was determined by single crystal X-ray analysis.