1. Thiazolidinediones: an update
2. Note: Three mechanistic possibilities were proposed to describe the formation of the key intermediate observed in the kinetic studies. Density functional theory calculations (B3LYP/6-31G(d)) were carried out on simpler model systems to explore these mechanisms. The first two mechanisms proposed a rearrangement of the substituent from N2 to N1 ofIvia a five-membered ring transition state as shown in Figure 10. The computed activation energy barrier (Eact) for this rearrangement was extremely high (∼68 kcal/mol). This can be attributed to the overwhelming strain involved in the five-membered ring transition state to achieve the N2 to N1 rearrangement. Transition structure geometry and activation energy barrier for the proposed N2 to N1 rearrangement via five-membered ring transition state.The third mechanism proposed the disproportionation ofII(see Figure 7) via a Grobe type fragmentation as shown followed by a fast cage recombination to form the intermediate. The computed activation energy barrier (Eact) for this fragmentation is 3.9 kcal/mol in ε = 37.2, the dielectric constant for DMF (3.4 kcal/mol in the gas phase, ε = 1). This implies that this proposed mechanism is indeed feasible and consistent with the observed experimental data. Transition structure geometry and activation energy barrier for the proposed Grobe fragmentation in the rate-limiting step of the reaction.
3. Base-Promoted in Situ Generation of Methyl Acrylate from Dimethyl 3,3‘-Dithiodipropionate. Application to N-Alkylation of Heterocycles