Bicydo 3.2.1 octenones

The fadal diastereoselectivity of intermolecular cyclopentenone [2 + 2]-photocy-cloaddition reactions is predictable if the cyclopentenone or a cyclic alkene reaction partner is chiral. Addition occurs from the more accessible side, and good stereocontrol can be expected if the stereogenic center is located at the a-position to the double bond. In their total synthesis of ( )-kelsoene (11), Piers et al. [22] utilized cyclopentenone 9 in the [2 + 2]-photocycloaddition to ethylene (Scheme 6.5). The cyclobutane 10 was obtained as a single diastereoisomer. In a similar fashion, Mehta et al. have frequently employed the fact that an approach to diquinane-type cis-bicydo [3.3.0]octenones occurs from the more accessible convex face. Applications can be found in the syntheses of (+)-kelsoene [23], (—)-sulcatine G [24], and ( )-merri-lactone A [25]. 

In addition, the Baeyer-Villiger oxidation of racemic bicydo[3.2.0]-hept-2-en-6-one with E. coli pQR209 gives about 50% of nearly enantiomerically pure (lR,5S)-3-oxabicyclo octenone as shown in Fig. 6 this regioisomer cannot be made selectively by chemical Baeyer-Villiger oxidation. In both cases, a yield of product on substrate of 85 to 90% has been obtained. Applying a ketone feed rate which keeps the reactant concentration below the inhibitory concentration was essential. 

Pauson-Khand reaction to prepare bicydo[3.3.0]octenones proceeds... 

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