ChemInform Abstract: Cyclopropenium Ion Catalyzed Beckmann Rearrangement.

Catalysts or Initiators? Beckmann Rearrangement Revisited

“…Second, the Meisenheimer complex does not exist in the CPI-Cl system, as R migration of I-2 forms 5, I-8, and Cl − (pathway II, Scheme 3), rather than species 4 in Scheme 2. Since I-8 was not experimentally detected as an intermediate, 7 pathway II is unlikely to occur. In addition, for pathway III, although the rate-limiting barrier for the conversion 5 + I-3 → 7 + CPI is lower than those for the systems in Scheme 2 (ΔΔG ≠298 = 14.8 kcal/mol versus ΔΔG ≠298 > 20 kcal/mol; Figure 2 and Table 1), the overall rate-limiting barrier for the catalytic cycle of pathway III is still higher than that of pathway I (ΔΔG ≠298 = 28.7 kcal/mol for R + CPI → 7 + CPI versus ΔΔG ≠298 = 18.1 kcal/mol for R + 5 → 7 + 5; Figure 2).…”