Formation of medium-size bridged ring systems via ring-closing metathesis of 2,5-disubstituted-2,3-dihydro-1H-pyrroles

A series of 2,5-disubstituted-2,3-dihydro-1H-pyrroles were prepared via diastereoselective alkylations of sulfone 10. Ring-closing metathesis (RCM), using Grubbs' catalyst, provided bridged ring systems with newly formed 9- to 12-membered rings in moderate to good yields. The 9-membered ring was formed as a single Z-isomer whereas the 10- to 12-membered rings were formed as mixtures of E- and Z-isomers. It was shown that the minor diastereomer obtained from the alkylation product 11c failed to undergo RCM, illustrating the crucial aspect of substrate conformation.