Reaction of a variety of C
CH bond-containing 1,6-enynes with N
2CHSiMe
3 in the presence ofRuCl(COD)Cp* as catalyst precursor
leads, at room temperature, to the general formation of alkenylbicyclo[3.1.0]hexanes with high
Z-stereose
lectivity of the alkenyl group and
cis arrangement of the alkenyl groupand an initial doub
le-bond substituent, for an
E-configuration of this doub
le bond. The stereochemistry isestablished by determining the X-ray structures of three bicyclic products. The same reaction with 1,6-enynes bearing an R substituent on the C
1 carbon of the trip
le bond results in either cyclopropanation ofthe doub
le bond with bulky R groups (SiMe
3, Ph) or formation of alkylidene-alkenyl five-memberedheterocyc
les, resulting from a
le"> elimination process, with
less bulky R groups (R = Me, CH
2CH=CH
2).The reaction can be applied to
in situ desilylation in methanol and direct formation of vinylbicyclo[3.1.0]hexanes and to the formation of some alkenylbicyclo[4.1.0]heptanes from 1,7-enynes. The catalytic formationof alkenylbicyclo[3.1.0]hexanes also takes place with enynes and N
2CHCO
2Et or N
2CHPh. The reactioncan be understood to proceed by an initial [2+2] addition of the Ru=CHSiMe
3 bond with the enyne C
CHbond, successively
leading to an alkenylruthenium-carbene and a key alkenyl bicyclic ruthenacyclobutane,which promotes the cyclopropanation, rather than metathesis, into bicyclo[3.1.0]hexanes. Density functionaltheory calculations performed starting from the model system Ru(HC
CH)(CH
2=CH
2)Cl(C
5H
5) show thatthe transformation into a ruthenacyclobutane intermediate occurs with a temporary
3-coordination of thecyclopentadienyl ligand. This step is followed by coordination of the alkenyl group, which
leads to a mixedalkyl-allyl ligand. Because of the non-equiva
lence of the terminal allylic carbon atoms, their coupling favorscyclopropanation rather than the expected metathesis process. A direct comparison of the energy profi
leswith respect to those involving the Grubbs catalyst is presented, showing that cyclopropanation is favoredwith respect to enyne metathesis.