Chemo enzymatic synthesis of Rengyol and Isorengyol

Abstract: Cyanohydrins 2 of O-protected 4-hydroxycyclohexanones 1 are excellent starting compounds for the synthesis of Isorengyol ( I ) and Rengyol ( II ). The cyano group of the O-benzyl derivative 2d is first converted into the corresponding aldehyde 4 , which via Wittig olefination led to the vinyl compound 6 . Hydroboration of the trans-derivative ( trans-6 ) leads, after debenzylation, to Isorengyol, whereas hydroboration and debenzylation of the cis-isomer ( cis-6 ) gives Rengyol. With hydroxynitrile lyases (HNLs) as catalysts the stereoselective preparation of cis- as well as trans-cyanohydrin 2d is possible, which enables the selective preparation of Isorengyol or Rengyol, respectively. The trans-configuration of Isorengyol and the cis-configuration of Rengyol were secured by X-ray crystal structure analysis. [Copyright &y& Elsevier]