118. P. Müller, P. Polleux,
     “Enantioselective Formation of Bicyclic Lactones by Rhodium-Catalyzed Intramolecular CH-insertion reactions”
     Helv. Chim. Acta 1994, 77, 645-654.

The decomposition of cyclohexyl diazoacetate (5a) in the presence of the chiral [Rh₂{(2S)-mepy}₄] catalyst leads to a 3:1 cis/trans mixture of bicyclic lactone 6a with an enantiomeric excess of 95–97% (cis) and 90% (trans). The conformationally rigid tert-butyl derivatives 5b and 5cafford, in the presence of the same catalyst, 6b and 6c, respectively, via insertion into the equatorial CH bonds exclusively, with ee's ofca. 95%. A remarkable degree of induction (92–95%) results in the lactone 6g upon decomposition of 1-isopropyl-2-methylpropyl diazoacetate (5g). The diazoacetates derived from 1-methylcyclohexanol, cyclopentanol and 1-methylcyclopentanol (5d–f) afford under similar conditions insertion products with higher diastereoselectivity, but significantly lower enantioselectivity. Other dirhodium catalysts are less efficient.

DOI : 10.1002/hlca.19940770307 

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