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Synthesis of trans-3,4-Dimethyl-4-(3-hydroxyphenyl)piperidine Opioid Antagonists:  Application of the Cis-Thermal Elimination of Carbonates to Alkaloid Synthesis

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posted on 26.01.1996, 00:00 by John A. Werner, Louis R. Cerbone, Scott A. Frank, Jeffrey A. Ward, Parviz Labib, Roger W. Tharp-Taylor, C. W. Ryan
Improved syntheses of two trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine opioid antagonists from 1,3-dimethyl-4-piperidinone are described. The 1,3-dimethyl-4-arylpiperidinol 23 was selectively dehydrated in a two step process to the 1,3-dimethyl-4-aryl-1,2,3,6-tetrahydropyridine 26 by the cis-thermal elimination of the corresponding alkyl carbonate derivative at 190 °C. In the presence of a basic nitrogen, the success of the elimination was found to be critically dependent upon the nature of the carbonate alkyl group, with Et, i-Bu, and i-Pr being preferred (90% yield). Alkylation of the metalloenamine, formed by deprotonation of 26 with n-BuLi, proceeded regio- and stereospecifically to give the trans-3,4-dimethyl-4-aryl-1,2,3,4-tetrahydropyridine 27, which was converted in three steps to the common intermediate, (3R,4R)-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine. LY255582, a centrally-active opioid antagonist, and LY246736-dihydrate, a peripherally-active opioid antagonist, were prepared from 1,3-dimethyl-4-piperidinone in 11.8% yield (8 steps) and 6.2% yield (12 steps), respectively.

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