Diels-Alder Cycloaddition of Tetraphenylcyclopentadienone and 1,3,5-Hexatriynes

Diels-Alder cycloaddition reactions of 1,3,5-hexatriynes with tetraphenylcyclopentadienone have been performed, and mainly gave 1,2-diethynyl-3,4,5,6-tetraphenylbenzene derivatives as products. The Diels-Alder reactions were optimized under conventional heating and microwave irradiation conditions, and showed good selectivity towards the central carbon-carbon triple bond of the triyne. Empirical evidence suggests that the selectivity of the reaction is governed predominantly by the steric demands of the end-groups of the triyne. Several of the Diels-Alder products could be further elaborated by a sequence of desilylation and oxidative homocoupling to provide dimeric products. The homocoupling reaction was optimized by Pd catalysis. The X-ray crystallographic analysis of two derivatives is reported. Diels-Alder cycloaddition reactions of 1,3,5-hexatriynes with tetraphenylcyclopentadienone under either thermal or microwave-assisted conditions give regioisomeric products that can be interpreted based on the size of the triyne end-groups.