Phenols, from cyclobutenones

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/... 

Kondo T, Niimi M, Nomura M, Wada K, Mitsudo TA (2007) Rhodium-catalyzed rapid synthesis of substituted phenols from cyclobutenones and alkynes or alkenes via C-C bond cleavage. Tetrahedron Lett 48(16) 2837-2839, http //dx.doi.Org/10.1016/j.tetlet.2007.02.091... 

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 ". ... 

Huffman MA, Liebeskind LS (1990) Insertion of (.eta.5-indeny)cobalt(I) into cyclobutenones the first synthesis of phenols from isolated vinylketene complexes. J Am Chem Soc 112... 

Highly functionalized phenols 131 starting materials for an indium tri-flate-induced ring closure are available from cyclobutenones 130 which with activated methylene ketones give the acridines 132 (2012JOC5173), Scheme 48. 

Andriamiadanarivo, R., Pujol, B., Chantegrel, B., Deshayes, C., and Doutheau, A., Preparation of functionalized cyclobutenones and phenolic compounds from a-diazo P-ketophosphonates, Tetrahedron Lett., 34, 7923, 1993. 

Phenol synthesis. In the presence of this Ni(0) catalyst cyclobutenones can couple with internal alkynes to form phenols in 50-80% yield. Two phenols are obtained from unsymmetrical alkynes with only slight regioselectivity based on the size of the alkyl substituents. Modest selectivity obtains with oxygen-substituted alkynes. 

This phenol synthesis differs from the thermal reaction of cyclobutenones with alkynes (15, 160) in that activated alkynes are not required and the ultimate positions of the alkyne substituents in the phenol are different. 

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