Supersonic jet studies of alkyl-substituted pyrazines and pyridines. Minimum energy conformations and torsional motion
Conformational reference for methyl-, ethyl-, propyl-, and isoproply-substituted pyrazines and pyridines are determined by mass resolved excitation spectroscopy (MRES) and MOPAC 5/PM3 semiempirical calculations. The results of these studies suggest that the conformational behavior of alkyl-substituted pyrazines and pyridines is different from that of alkyl-subtituted benzenes. Based on the experimental and semiempirical theoretical results reported herein and published ab initio calculations, this difference can be attributed to a stabilizing interaction between an α-hydrogen atom of alkyl subsituted and the adjacent lone pair nonbonding electrons on the ring nitrogen atom.
Seeman, Jeffey I.,Paine III, John B.,Secor, Henry V.,Im, Hoong-Sun,Bernstein
p. 5269 - 5280
(2007/10/02)
The Wolff-Kishner Reduction of 2-Acetonyl Pyrazines and Pyridines. A Novel Rearrangement
Wolff-Kishner reduction of 1-(6-methylpyrazin-2-yl)-2-propanone leads to the formation of 2-isopropyl-6-methylpyrazine (2a), in addition to the expected 6-methyl-2-n-propylpyrazine.The by-product 2a is suggested to arise via a spirocyclopropylidene aza-anion, which serves as a conduit between the initial less-stable secondary 1-(2-pyrazinyl)-2-propyl carbanion and the more stable primary 2-(2-pyrazinyl)-1-propyl carbanion.Similar results were observed for the 1-(3-methylpyrazin-2-yl) and 1-(6-methylpyridin-2-yl)-2-propanones.The extent of by-product formation diminished in the pyridine ring system.Electrophilic activation of the ring appears essential since the benzene ring analog phenylacetone gave no detectable cumene under identical reaction conditions.
Paine III, John B.
p. 1463 - 1465
(2007/10/02)
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