Nickel cyclobutenones

Substituted phenols are synthesized by the nickel(0)-catalyzed ring opening of cyclobutenones and subsequent [4+2]cycloaddition with alkynes [106]. 

Complexes formed from tantalum(V) chloride or niobium(V) chloride, alkynes and zinc undergo analogous reactions. Mixtures of phenols are obtained from cyclobutenones and alkynes in the presence of nickel(cyclooctadiene)2 at 0°C. Thus 4-methyl-3-phenylcyclobut-2-enone and 4-methylpent-2-yne yield 593 and 594 ". ... 

Reactions between cyclobutenones and alkynes in order to synthesize phenols have also been studied by Danheiser and coworkers [equation 8]. In particular, R = CH3O, CH3S, (CH3)2N and (CH3)3SiO are favourable substituents . The trimethylsilyloxy-substi-tuted alkyne furnishes a trimethylsilylresorcinol from which the trimethylsilyl group is easily removed. A nickel(0)-catalysed version of this synthesis of phenols from cyclobutenones and alkynes was published by Huffman and Liebeskind. ... 

Huffman MA, Liebeskind LS (1991) Nickel(0)-catalyzed synthesis of substituted phenols from cyclobutenones and alkynes. J Am Chem Soc 113(7) 2771-2772. doi 10.1021/... 

Alkyne insertion was achieved using a nickel(0) catalyst [59]. The cyclobutenone-alkyne coupling reaction provided substituted phenols (Scheme 3.50). Unhke the thermal reaction, unactivated alkynes readily participated in aimulation. Regioselectivity of alkyne insertion was low. 

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