This paper describes a new approach in transition-metal-catalyzed unsymmetric cycloisomerization for medium-sized heterocycles. The steric and electronic effects of an NHC–NiH catalyst and γ-heteroatom chelation were used together as a basis for 1,n-diene termini differentiation and for nγ-exo-trig (head-to-tail) product selectivity. Heterocycles bearing an exocyclic methylene such as oxepines, thiepines, siloxepines, and oxocanes were synthesized from the corresponding 1,n-dienes by a fine-tuning of the NHC properties. The implication of the underlying hypothesis was further demonstrated in a competition experiment in which strained oxepines were formed preferentially over other competing oxa-/carbocycles. Under more forcing physical conditions and the use of a suitable NHC ligand, the exocyclic methylene products were isomerized further into endocyclic olefin products regioselectively in one pot.

Via a cooperation of NHC, Si substituents and a M center, β-Si elimination was attenuated, revealing a new way to attain a high Ni-β-SiR3:Ni-σ-SiR3 ratio. The scope is illustrated by a head-to-tail vinylsilane-α-olefin hydroalkenylation.

We have discovered a mild, catalytic protocol for the regio- and stereoselective synthesis of trisubstituted allyl diarylphosphonates from the corresponding disubstituted allyl silyl ethers, circumventing the challenges related to the preparation and availability of stereodefined trisubstituted olefins. A closely related arylation reaction was also discovered during the methodology development. By simply switching the reaction medium, high phosphonylation/arylation ratios and vice versa can be achieved. This may not be a direct result of changing solvent polarity. The allyl diarylphosphonates were evaluated as carboxylesterase inhibitors, and the screening results revealed that the inhibitory efficiency is highly related to the choice of alkenes and aryl substituents.

We have discovered a mild, catalytic protocol for the regio- and stereoselective synthesis of trisubstituted allyl diarylphosphonates from the corresponding disubstituted allyl silyl ethers, circumventing the challenges related to the preparation and availability of stereodefined trisubstituted olefins. A closely related arylation reaction was also discovered during the methodology development. By simply switching the reaction medium, high phosphonylation/arylation ratios and vice versa can be achieved. This may not be a direct result of changing solvent polarity. The allyl diarylphosphonates were evaluated as carboxylesterase inhibitors, and the screening results revealed that the inhibitory efficiency is highly related to the choice of alkenes and aryl substituents.

Via a cooperation of NHC, Si substituents and a M center, β-Si elimination was attenuated, revealing a new way to attain a high Ni-β-SiR3:Ni-σ-SiR3 ratio. The scope is illustrated by a head-to-tail vinylsilane-α-olefin hydroalkenylation.