The [3+2] cycloaddition reaction of a tungsten-containing carbonyl ylide with methyl vinyl ether and the insertion reactions of the nonstabilized carbene complex intermediates produced have been investigated through the use of B3LYP density functional theory. The [3+2] cycloaddition reaction of the tungsten-containing carbonyl ylide has been proven to proceed concertedly, reversibly, and with high endo selectivity. The intermolecular SiH insertion reactions of the carbene complex intermediates have been proven to be favored over the intramolecular CH insertion, in good agreement with experimental results. Moreover, the kinetic endo/exo ratio of the [3+2] cycloaddition reaction has been shown to determine the endo/exo selectivity of the SiH insertion products. In addition, secondary orbital interactions involving the benzene ring and the carbonyl ligand on the metal center have turned out to strongly influence the high endo selectivity of the [3+2] cycloaddition reaction with methyl vinyl ether.