A Convenient Synthesis of 2′,3′′′′-Dimethyl-p-sexiphenyl

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Abstract
Hitherto unreported 2′,3′′′′-dimethyl-p-sexiphenyl (6) is synthesized by an unambiguous route in good yield, starting from inexpensive commercially available biphenyl. The general reaction sequence consists of: (i) bischloromethylation of biphenyl, to give 4,4′-bis(chloromethyl)biphenyl (1) (ii) conversion of 1, to its bisphosphonium salt 2 (iii) a Wittig reaction of the salt with two equivalents of β-methylcinnamaldehyde to yield hitherto unreported 4,4′-bis(3-methyl-4-phenyl-buta-1,3-dienyl)biphenyl (3) (iv) the [4 + 2] cycloaddition of 3 with diethyl acetylenedicarboxylate to yield 4 (v) hydrolysis of 4 to 5 (vi) and oxidative decarboxylation of 5 with potassium hexacyano ferrate(III). All reactions which are simple and straightforward proceed in good yield, except the last step.

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