Nickel-mediated C(sp2)−O bond cleavage: Esters from the coupling of vinyl ethers or the cross-coupling of vinyl ethers with acetaldehyde

The complexes (Cy 3 P)Ni(ηSu et al. (2015) 6 -PhMe) and [(Cy 3 P) 2 Ni] 2 (μ-N 2 ) were utilized in a study of nickel C(sp 2 ) − O bond cleavage. Unexpectedly, a mixture of H 2 C=CHOEt with [(Cy 3 P) 2 Ni] 2 (μ-N 2 ) underwent a stoichiometric reaction upon heating to provide the ester MeCO 2 Et and (Cy 3 P) 2 Ni(ηLi et al. (2011) 2 -C 2 H 4 ). An extension of this reaction allowed for the cross-coupling of aldehydes and vinyl ethers to give esters. The vinyl adducts (Cy 3 P) 2 Ni(ηLi et al. (2011) 2 -H 2 C=CHOR), (R = t Bu, Cy, SiMe 3 ) were isolated and fully characterized. Other prospective intermediates, such as (Cy 3 P)Ni(ηLi et al. (2011) 2 -O=CHMe)(ηLi et al. (2011) 2 - t BuOCH=CH 2 ), were tentatively assigned by NMR spectroscopy. Calculations using density functional theory were performed to evaluate the relevance of proposed mechanistic manifolds. This work sets a foundation for the development of a novel selective methodology for aliphatic ester synthesis, as well as giving insight into C(sp 2 ) − O bond cleavage mechanisms accessible to Ni.