Catalyst free boron carbon bond cleavage and facile formation of five-membered PNBCC heterocycles. Issue 44 (25th October 2017) - Dasgupta, Rajarshi
Abstract : The [3 + 2] cycloaddition reaction of N (2, 6-iPr2 C6 H3 )(PPh2 )(BCy2 ) (1 ) with activated alkynes led to the boron, phosphorus containing five-membered heterocycles (2–4 ) with facile cleavage of B–C bond and concomitant formation of a P–C bond with an ylidic character. Abstract : The [3 + 2] cycloaddition reaction of phosphanyl aminoborane [ N (2, 6-iPr2 C6 H3 )(PPh2 )(BCy2 )] (1 ) with activated alkynes led to boron and phosphorus containing five-membered heterocycles [(2, 6-iPr2 C6 H3 )NPPh2 (CO2 R)C–C(Cy)(CO2 R)(BCy)] [R = Me (2 ), Et (3 ) and H (4 )] with facile cleavage of the B–C bond and concomitant formation of a P–C bond with an ylidic character. DFT calculations indicate that1 can be considered as a non-conjugated 1, 3-dipole having two reaction centers viz ., a nucleophilic P-center and an electrophilic B-center. The reaction of1 with the alkynes proceeds through a stepwise dipolar addition mechanism, followed by the migration of the cyclohexyl group from the B-atom to the adjacent C-atom.