Introduction. -The 1-azabicyclo[2.2. llheptane (1) was first prepared by Prelog and Clemo [l] in 1936. In the last few years, there has been great interest in this skeleton for preparing rigid structural analogues of biogenic amines (for acetylcholine analogues, see [2a-k]; for serotonine analogues, see [21-n]). In derivatives of 1 in which the 3-position is substituted with an ester isostere, the gauche conformation of acetylcholine is mimicked. The 3-exo-(l,2,4-oxadiazolyl) derivatives of 1-azabicyclo[2.2. llheptane were claimed to be among the most potent muscarinic agonists known [3]. When we started our work in this area, all chiral compounds in this series had been reported as racemates [2]. Very recently, methods for resolving l-azabicyclo[2.2.l]heptane-3-carboxylates as their diastereoisomeric amides [4] were disclosed, as well as the synthesis of (+)-(3S,4R)-ethyl l-azabicyclo[2.2.l]heptane-3-carboxylate [5]. For a suitable comparison of the biological activity of these and similar compounds with that of other muscarinic agonists in our models [6], we needed the compounds in enantiomerically pure form and knowledge of their absolute configuration.We, therefore, synthesised both enantiomers of 3-( 1,3-dithian-2-ylidene)-l-azabicyclo[2.2. llheptane ((+)-and (-)-5), a key intermediate in the synthesis of a large number of cholinergic agonists [2a], and determined their absolute configurations both using CD spectroscopy and X-ray crystallography.
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