Single crystal X-ray diffraction analysis of compounds A, B and, C helped us to assign the absolute configurations of the enantiomers of the bicyclo[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-npropylammonium 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.
The efficient conversion of 3-hydroxy-6-alkenoic acids into bicyclo[3.2.0]hept-3-en-6-ones by treatment with potassium acetate in acetic anhydride makes these I~,T-unsaturated bicyclic ketones easy available to be employed as useful starting materials or intermediates in synthesis of complex molecules. 2 Bicyclo[3.2.0]hept-3-en-6-ones possess an appealing structure with two fused rings of different size, each functionalized in a different manner, thus allowing for chemio-, regio-and stereoselective transformations.
Recently we found useful applications of these interesting building blocks in the synthesis of different natural products such as grandisol, 2 lineatin, 2 filifolone 3 and some important lactone intermediates for the synthesis of triquinane sesquiterpenes. 3
The synthetic potential and usefulness of bicyclo[3.2.0]hept-3-en-6-ones will be greatly enhanced if a procedure to have them enantiomerically pure would be developed. Recently, we have reported that the mechanism of the bicyclization precludes the EPC synthesis of bicyclo[3.2.0]hept-3-en-6-ones starting from enantiomerically pure 3-hydroxy-6-alkenoic acids. 4
This paper reports the results of our eflbrts to prepare pure enantiomers of bicyclo[3.2.0]hept-3-en-6ones 1-3 and bicyclo[3.2.0]hept-3-en-6-endo-ols 4-6, their optical properties, and the assignment of absolute