26345-14-2Relevant academic research and scientific papers
Methyl orthocarboxylates as methylating agents of heterocycles
Janin, Yves L.,Huel, Christiane,Flad, Genevieve,Thirot, Sylvie
, p. 1763 - 1769 (2002)
Methylation reactions occurring between trimethyl orthocarboxylates or N,N-dimethylcarboxamide dimethyl acetals and various hydroxylated heterocycles, involving a lactam-lactim tautomeric equilibrium, were investigated as an alternative to classic methyla
Regioselective photocycloaddition of pyridine derivatives to electron-rich alkenes
Sakamoto, Masami,Sano, Takeru,Fujita, Shohei,Ando, Masaru,Yamaguchi, Kentaro,Mino, Takashi,Fujita, Tsutomu
, p. 1447 - 1450 (2003)
Irradiation of a benzene solution of 3-cyano-2,6-dimethoxypyridine in the presence of ethyl vinyl ether (EVE) gave 1:1 photoadducts, 3-cyano -5-ethoxy-2,8-dimethoxy-4,5-dihydroazocine, in good yields, whose structure was established by X-ray single-crystal analysis. The photoadduct was produced via cycloaddition between the C3-C4 position of the pyridine derivatives and an alkene chromophore. On the other hand, 3-cyano -2,6-dimethoxy-4-methylpyridine cycloadds to EVE at the C2-C3 position of the pyridine ring upon irradiation. The difference is explained on the basis of the steric effect.
Conformational control and photoenolization of pyridine-3-carboxaldehydes in the solid state: Stabilization of photoenols via hydrogen bonding and electronic control
Mal, Prasenjit,Lourderaj,Parveen,Venugopalan,Moorthy, J. Narasimha,Sathyamurthy
, p. 3446 - 3453 (2007/10/03)
We have investigated the solid-state photobehavior of a broad set of pyridine-3-carboxaldehydes 1-5. The introduction of a heteroatom into mesitaldehydes as in aldehydes 1 raises the question of conformational preference in the solid state. The preferred conformations have been unequivocally established from X-ray crystal structure analyses of two of the aldehydes, 1c and 2c; it is shown that intramolecular hydrogen bonding could be utilized to achieve conformational control. In contrast to mesitaldehydes, which undergo efficient photocyclization to benzocyclobutenols in the solid state, the heteroatom analogues 1b and 1c exhibit a perceptible color change (from colorless to pale yellow for 1b and yellow-orange for 1c) upon UV irradiation; the color attributed to (E)-enols is persistent for several hours. Continued irradiation leads to an intractable polymeric material. The AM1 calculations, which have been reliably applied to the thermal cyclization of xylylenols to benzocyclobutenols, reveal that the (E)-enols of 1 are more stable than those of the mesitaldehydes relative to their corresponding benzocyclobutenols. The stabilization is interpreted as arising from the possibility of engaging the heteroatom in resonance delocalization. That the contribution from such a role of the nitrogen atom is so pronounced is elegantly demonstrated by forming the fluoroborate salts; 1a-HBF4 and 1b-HBF4 readily exhibit highly red-shifted absorption upon exposure to UV radiation as a result of stabilization of the photoenols. Notably, such a remarkable stabilization via electronic control of the photoenols is unprecedented. All of the 2-methoxy- and 2-chloro-substituted aldehydes 2-5 exhibit photochromism. Ab initio calculations show that the methoxy group in aldehydes 2 and 3 stabilizes the (E)-enols via O-H...O hydrogen bonding as compared to those of 1 by 5-6 kcal/mol relative to their corresponding benzocyclobutenols. Thus, the presence of methoxy and halo groups at position 2 serves not only to direct the formyl oxygen toward the methyl group for H-abstraction but also to stabilize the (E)-enols.
