Mechanistic Studies on the O-Directed Free-Radical Hydrostannation of Disubstituted Acetylenes with Ph3SnH and Et3B and on the Iodination of Allylically Oxygenated α-Triphenylstannylalkenes
摘要:
The free-radical hydrostannation of 1 with Ph3SnH and catalytic Et3B in PhMe has been mechanistically probed. At high Ph3SnH concentrations, the O-directed hydrostannation pathway dominates, and 2 is formed with good selectivity (ca. 11.1:1). Substantially lower stannane/substrate concentrations increase the amount of tandem 5-exo-trig cyclization product 3 that is observed.
The cleavage of R2SiXY (R = alkyl, phenyl; X = H, Cl, Y = α-Np, Ph, Cl, H) by triflic acid is selective, leading to new difunctional silyltriflates, R2SiXOTf, with the relative ease of cleavage of Si-Y being, α-Np>Ph>Cl>H⪢Me, Et, But.