Cyclo-Prins reaction

Methylenebicyclo [3.3.1] nonan-7-one dissolved in ethyl mercaptan, a little HGl introduced, and refluxed 3 hrs. l-hydroxy-3-ethylmercaptoadamantane. Y 79%. F. e., also 1,3-dihydroxyadamantane by cyclo-Prins reaction, s. H. Stetter, J. Gartner, and P. Tacke, B. 98, 3888 (1965). 

The process from the FMC company involves as the pivotal step an intramolecular stereoselective [2 + 1 [-cycloaddition. In a Prins reaction [94] of chloral and isobutene, followed by an isomerisation, a racemic, trichloromethyl-substituted aUyl alcohol is obtained. Reaction with the isocyanate from (R)-naphthylethyl-amine enables separation ofthe diastereomers by crystallisation. The carbamate is cleaved by trichlorosilane/triethylamine, thus permitting the recycling of the chiral auxiliary. The optically pure (R)-aUyl alcohol is reacted with diketene, to produce the / -keto-ester. After diazo transfer and basic cleavage, the diazoacetate is obtained catalysed by a copper salt, this is converted in a [2 + 1 ]-cyclo-addition into a bicyclic lactone. The Boord reaction (discovered by Cecil E. Boord in 1930) [95] finally gives (IR)-cis-permethric acid. [96]... 

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