Palladium-catalyzed allene synthesis enabled by β-hydrogen elimination from sp2-carbon

Abstract

The rational design based on a deep understanding of the present reaction mechanism is an important, viable approach to discover new organic transformations. β-Hydrogen elimination from palladium complexes is a fundamental reaction in palladium catalysis. Normally, the eliminated β-hydrogen has to be attached to a sp3-carbon. We envision that the hydrogen elimination from sp2-carbon is possible by using thoroughly designed reaction systems, which may offer a new strategy for the preparation of allenes. Here, we describe a palladium-catalyzed cross-coupling of 2,2-diarylvinyl bromides and diazo compounds, where a β-vinylic hydrogen elimination from allylic palladium intermediate is proposed to be the key step. Both aryl diazo carbonyl compounds and N-tosylhydrazones are competent carbene precursors in this reaction. The reaction mechanism is explored by control experiments, KIE studies and DFT calculations.

Pd/Xu-Phos-catalyzed asymmetric elimination of fully substituted enol triflates into axially chiral trisubstituted allenes

“…5B) (51). To deeply understand the reaction mechanism (12,52,53), DFT calculations were carried out with the Gaussian 09 software package (54)(55)(56)(57). Calculation details were provided in the Supplementary Materials.…”

Pd-Catalyzed Coupling of N-Tosylhydrazones with Benzylic Phosphates: Toward the Synthesis of Di- or Tri-Substituted Alkenes

“…The precipitates were filtered, washed with a small quantity of MeOH and diethyl ether, and then were dried in vacuo to afford the corresponding pure NTHs 2 . N ′-(Diphenylmethylene)-4-methylbenzenesulfonohydrazide 2a , N ′-(bis­(4-methoxyphenyl)­methylene)-4-methylbenzenesulfonohydrazide 2b , N ′-(bis­(4-fluorophenyl)­methylene)-4-methylbenzenesulfonohydrazide 2c , 4-methyl- N ′-(phenyl­( m -tolyl)­methylene)­benzenesulfonohydrazide 2d , N ′-((4-fluorophenyl)­(phenyl)­methylene)-4-methylbenzenesulfonohydrazide 2e , 4-methyl- N ′-(phenyl­(4-(trifluoromethyl)­phenyl)­methylene)­benzenesulfonohydrazide 2f , N ′-((4-methoxyphenyl) (phenyl)­methylene)-4-methylbenzenesulfonohydrazide 2g , N ′-((3-chlorophenyl)­(phenyl)­methylene)-4-methylbenzenesulfonohydrazide 2h , N ′-((4-bromophenyl)­(phenyl)­methylene)-4-methylbenzenesulfonohydrazide 2i , N ′-(4-methoxybenzylidene)-4-methylbenzenesulfonohydrazide 2j , 4-methyl- N ′-(3,4,5-tri­meth­oxy­benzyl­idene)­benzene­sulfono­hydrazide 2k , N ′-(3,5-dimeth­oxy­benzyl­idene)-4-methyl­benzene­sulfono­hydrazide 2l , N ′-((2,3-dihydro­benzo­[ b ]­[1,4]­dioxin-6-yl)­methylene)-4-methyl­benzene­sulfono­hydrazide 2m , 4-methyl- N ′-(naphthalen-2-ylmeth­ylene)­benzene­sulfono­hydrazide 2n , N ′-(4-fluoro­benzyl­idene)-4-methyl­benzene­sulfono­hydrazide 2o , 4-methyl- N ′-(4-nitro­benzyl­idene)­benzene­sulfono­hydrazide 2p , N ′-(9 H -fluoren-9-ylidene)-4-methyl­benzene­sulfono­hydrazide 2q , N ′-(3,3-di­methyl­butan-2-ylidene)-4-methyl­benzene­sulfono­hydrazide 2r , and 2s were reported in previous literature studies.…”

Palladium-catalyzed and ligand-controlled divergent cycloadditions of vinylidenecyclopropane-diesters with para-quinone methides enabled by zwitterionic π-propargyl palladium species

“…Next, we continued to investigate the following reaction steps involving the proton transfer assisted by base from intermediate Int4 (Scheme 6b). 14 At this stage, two alternative pathways are investigated, respectively. One of them is path a involving the base coordinated to the palladium and the other is path b involving the direct proton transfer and no coordination between the base and the palladium.…”