TETRAHEDRON LETTERS Pergamon Tetrahedron Letters 39 (1998) 1261-1264 Alkali metal hydride or aqueous hydroxide induced conjugate addition of trimethylsilyl enol ethers to enones. • # A convenient alternative to Lewis acid mediated reaction. Vishwanath M. Swamy and Amitabha Sarkar* DivisionOf OrganicChemistry(Synthesis) National ChemicalLaboratory Pune - 411 008, India. Received 28 October 1997; revised 2 December 1997; accepted 5 December 1997 Abstract : Conjugateaddition to enones by enolates derived from baseqnducedcleavage of O-Si bond of trimethylsilyl enol ethers, yields 1,5-dicarbonyl compoundsin good yields. © 1998ElsevierScienceLtd. All rights reserved. Titanium chloride mediated addition of silyl enol ethers to a,~-unsaturated compounds was first reported in 1974 ~. This reaction is an important carbon-carbon bond forming reaction and stands out for its advantages in terms of selectivity, regiospecificity and suppression of side reactions, over addition of lithium enolates2 to enones. Since then, other Lewis acids like BFa.OEt23, SnCl4,4 lanthanide triflates and scandium triflate5, have been reported to catalyse this reaction. Even trityl salts6, Montmorillonite clay 7, CsF a mediate such reactions to provide 1,5 diketones in high yields. These diketones are useful intermediates for the synthesis of substituted cyclohexenones 9 , pyridinesl°a and selenium~°b and phosphorous l°c containing heterocycles. Water is scrupulously avoided in all these reactions for obvious reasons ever since Stork described the generation of enolates from silyl enol ethers by the use of methyl lithium11. Lubinuea, however, has shown that silyl enol ethers undergo Mukaiyama aldol reaction with aldehydes in water without a catalyst over a period of several days lz. We now find that simple and readily available base like NaOH or KH can cleave silyl enol ethers such that the enolates generated in situ can efficiently add to enones in a conjugate manner in a much shorter time. A biphasic condition using 50% aq. NaOH and dichloromethane with 10 mol% of tetrabutylammonium bromide as a phase transfer catalyst, was used in the reactions initially performed. In a few instances a molar equivalent of potassium hydride in DMF was also effective (Table-l, condition B). All reactions were conducted at room temperature and completion of reaction was monitored by TLC. The reaction is facile with aromatic as well as aliphatic silyl enol ethers. The reaction works well even with ferrocene enones 5 and 6. The structures of the products were satisfactorily determined by 1H and IaCNMR spectroscopy, and were supported by elemental analyses. 0040-4039/98/$19.00 © 1998 Elsevier Science Ltd. All rights reserved. PH: S0040-4039(97)10771-7