Substituent effects for the BF₃‐mediated reactions of allyltributyltin and allyltriethyllead with benzaldehyde

Abstract

Substituent effects were measured for the reactions of substituted benzaldehydes with allyltributyltin (1) and allyltriethyllead (2) reagents in the presence of BF,*OEt, in CH,CI,. The Hammett p values were small and positive at 25°C and negative at -78°C for both 1 and 2. These could be interpreted in terms of the contribution of electrophilic complexation between the aldehyde function and BF, as a rate-limiting step. A large negative p value was observed for the complex-formation equilibria between substituted benzaldehydes and BF,.

Beyond static structures: Putting forth REMD as a tool to solve problems in computational organic chemistry

“…[1,2] The literature is rife with examples of reaction pathways in which reactants, intermediates, and products, as well as their associated transition states, are cartooned as a series of static geometries each possessing a specific reaction enthalpy. Often, a picture of this type successfully captures the key aspects of a system allowing, for example, identification of the primary mechanistic pathway [3][4][5][6][7][8][9] or rationalization of the presence of a specific intermediate. [9][10][11][12][13] Such descriptions, however, are occasionally insufficient to chemistry occurring in an experimental setting, [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] in the most extreme cases leading to disastrous failures.…”

Kinetic study of BH3 reduction of benzaldehydes: identification of effective reducing species

“…The initial complex formation is an electrophilic reaction of BH 3 , and thus a ρ value on this equilibrium should be negative. Indeed, it was reported that the Hammett ρ value for the complex‐formation equilibrium between 1‐X and BF 3 in CH 2 Cl 2 was largely negative (−3.5 at −78 °C) . Although BF 3 is a much stronger acid and therefore forms a much stronger complex with aldehyde than BH 3 , the result clearly indicated that the complex formation is a strongly electrophilic process.…”

Dynamic control of dichlorocarbene addition to cyclopropene

“…[3] The energetics of the CCl 2 -cyclopropene systemthat is, a near-negligible barrier to addition (<2 kcal/mol), substantial exothermicity (ΔH = −65 to −78 kcal/mol to form 2; ΔH = −83 to −106 kcal/mol to form 5), and post-TS branching of the reaction pathsled us to propose that CCl 2 addition to cyclopropene, and therefore the experimental product ratio, is controlled by nonstatistical reaction dynamics. [3] Previous instances of a single TS leading to multiple products [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] on a potential energy surface containing a plateau [20][21][22][23][24][25][26][27] have been attributed to dynamic control [28][29][30][31][32][33] of these reactions as well.…”