Pure enantiomers of bicyclo[3.2.0]hept-3-en-6-ones and bicyclo[3.2.0]hept-3-en-6-endo-ols: Resolution, absolute configuration and optical properties

Single crystal X-ray diffraction analysis of compounds A, B and, C helped us to assign the absolute configurations of the enantiomers of the bicycle [3.2.0]hept-3-en-6-endo-ols 4-6. These bicyclic alcohols were easily obtained by: (i) stereoselective reductions of the bicyclo[3.2.0]hept-3-en-6-ones 1-3, (ii) conversion into diastereoisomeric pairs using (-)-(1S,4R)-camphanic acid chloride as resolving agent, (iii) an efficient separation of diastereoisomers by flash-chromatography and, finally, (iv) a mild alkaline hydrolysis. The oxidation of pure enantiomers of the bicyclo[3.2.0]hept-3-en-6-endo-ols 4-6 with tetra-n-propylammonium perruthenate (TPAP) and N-methylmorpholine N-oxide (NMO) as co-oxidant furnished enantiomerically pure bicyclo[3.2.0]hept-3-en-6-ones 1-3. The different mutual disposition of carbonyl groups in the structure A and B justifies the different IR (KBr) signals for the carbonyls of each diastereoisomer.