The investigation of substituent effects in the double diastereotopic differentiation of substituted α-diazophosphonates using intramolecular cyclopropanation catalyzed by Rh2 (OAc) 4 is reported. Carbene facial selectivity in these transformations is dictated by substrate control in either of two ways:(i) exploitation of (R)-pantolactone as an auxiliary incorporated into the carboester functionality while probing olefinic substituent effects, or ( ...
