One‐Step Synthesis of Strained Bicyclic Carboxylic and Boronic Amino Esters via Ruthenium‐Catalysed Tandem Carbene Addition/Cyclopropanation of Enynes

The reaction of 1,6‐ and 1,7‐enynes, derived from carboxylic and boronic amino acids, with diazo compounds in the presence of the (cyclooctadiene)(pentamethylcyclopentadiene)ruthenium chloride complex RuCl(cod)(C₅Me₅)] catalyst leads to the formation of strained bicyclic proline or homoproline derivatives in good yields. This catalytic transformation proceeds under mild conditions, in one step from easily accessible enynes and was applied to various protecting groups. High stereoselectivities for the created alkenyl chain and excellent diastereoselectivities for proline derivatives were obtained.