Diastereoselective addition of monoterpenic alcoholates and thiolates to 2,3-dicarbomethoxynorbornadiene

Addition of excess lithium salts of (-)-menthol or (-)-borneol to 2,3-dicar bomethoxynorbornadiene 1 affords the transesterification-addition products 4 and 5. The thiols derived from the same monoterpenes give only the additi on products to the activated double bond, 6 and 7. In all cases, the additi on reaction is totally exo-selective with respect to the norbornadiene moie ty and moderately selective in discriminating the si- and re-face of the do uble bond. Both diastereomeric products are formed as a mixture of endo-exo epimers at C3. The major addition product of (-)-menthol to 1 is crystalli ne, of known absolute configuration, and has potential as a precursor of ch iral ligands. (C) 2000 Published by Elsevier Science Ltd.