Proline- and thioproline-derived enamines: The theoretical study of torsional and ring-puckering conformations

作者：Parasuk Wara****; Parasuk Vudhichai^*

来源：Computational and Theoretical Chemistry, 2011, 964(1-3): 133-140.

DOI：10.1016/j.comptc.2010.12.011

• DFT
• MP2
• Dispersion
• Thiazolidine
• Pyrrolidine
• Conformation
• Proline
• Thioproline
• Enamine

Praline and its derivatives catalyze Mannich and aldol reactions by forming enamine with ketone substrates. The conformations of such enamine play an important role in stereochemistry of the final products. In this study, the conformational features of praline- and thioproline-derived enamine which are derived from the reaction of cyclohexanone with (S)-praline and (R)-thioproline, respectively, are investigated theoretically using B3LYP and MP2. For praline-derived enamine, two ring-puckering conformations i.e. up (u) and down (d) puckered of pyrrolidine ring were located as minima. The conversion from d to u puckered conformation occurs via an envelop transition state requires 1.7 and 4.0 kcal/mol for syn and anti forms at MP2 level. The barriers of the rotation of C-sp2-N bond leading to syn and anti conformations are 3.8 and 4.3 kcal/mol for d and u ring-puckered forms, respectively. For thioproline-derived enamine, apart from the u and d puckered conformations of thiazolidine ring, a down and envelop (de) ring conformation was found as the global minimum. The barriers of the C-sp2-N bond rotation of d and u puckered ring are 3.5 and 4.3 kcal/mol, similar to the corresponding conformations of praline-derived enamine. The barriers of the ring puckering change from d to u are 0.7 and 4.1 kcal/mol for syn and anti form, respectively. An interesting characteristic of the de ring conformation is its small C-sp2-N bond rotation barrier of 2.3 kcal/mol.

• 出版日期2011-3