ORGN 484 |
Alpha,5-didehydro-3-picoline diradicals from skipped aza-enediynes: Computational and trapping studies of an aza-Myers-Saito cyclization
| Liping Feng, Dalip Kumar, and Sean M. Kerwin. Division of Medicinal Chemistry, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712 |
| The Myers-Saito cyclization of enyne allenes affords reactive diradical intermediates; however, the heteroatom substituted enyne allenes remain largely unexplored. Here we report our computational and experimental studies of the thermal rearrangements of aza-enyne allenes 2b-d derived from rearrangement of skipped aza-enediynes 1b-d. The results of (U)B3LYP/6-31G* calculations predict a facile isomerization of skipped aza-enediynes 1b-c to aza-enyne allenes 2b-c, and indicate that aza-Myers-Saito cyclization of aza-enyne allene 2b has a slightly lower predicted barrier and is slightly more exothermic than the Myers-Saito cyclization of 2a. In both cases, the resulting singlet diradical 3•• is much lower in energy than the closed-shell singlet zwitterion 3±. Aza-enyne allene 2d, obtained by isomerization of the skipped aza-enediyne, undergoes a rapid cyclization via either diraidcal 3d•• or zwitterion 3d± pathways, depending on the polarity of the solvent to afford the corresponding pyridine derivatives. In conclusion, we present the evidence for the existence of the previously unreported intermediate alpha,5-didehydro-3-picoline diradical (3d••) derived from 2d. 
|
| |
|
Total Synthesis, Process R&D, Combinatorial, Bioorganic, Physical Organic Chemistry
8:00 PM-10:00 PM, Tuesday, August 24, 2004 Pennsylvania Convention Center -- Hall D, Poster
Sci-Mix
8:00 PM-10:00 PM, Monday, August 23, 2004 Pennsylvania Convention Center -- Hall D, Sci-Mix
Division of Organic Chemistry
The 228th ACS National Meeting, in Philadelphia, PA, August 22-26, 2004
|