“…6- tert -Butyl-2,3-dimethyl-4(3 H )-pyrimidinone ( 1a ), 2-benzyl-6- tert -butyl-3-methyl-4(3 H )-pyrimidinone ( 1b ), and 6- tert -butyl-3-methyl-2-(4-methylbenzyl)-4(3 H )-pyrimidinone ( 1c ) were prepared from iodomethane and 6- tert -butyl-2-methyl-4(3 H )-pyrimidinone, 2-benzyl-6- tert -butyl-4(3 H )-pyrimidinone, and 6- tert -butyl-2-(4-methylbenzyl)-4(3 H )-pyrimidinone in alcoholic solutions containing base at 65−80 °C. The starting 4(3 H )-pyrimidinones were synthesized from the corresponding amidines and β-keto esters. 1f,h …”
Section: Methodsmentioning
confidence: 99%
“…The reactive and unstable photochemical intermediates are the valence-bond isomers (Dewar pyrimidinones) 2 , which react with the protic solvent molecules to give the 4-methoxy-2-azetidinone 3 in methanol, pyrimidinium-5-carboxylate 4 in acetic acid, imine 5 in methylamine, and enamide 6 in water or aqueous solution. However, irradiation of the 3-methyl-, 2,3-dimethyl-, and 3,6-dimethyl-4(3 H )-pyrimidinones in methanol did not give the expected 4-methoxy-2-azetidinone 3 , but, rather, a variety of the degradation products formed by the reactions of the labile imine Dewar pyrimidinones 2 with solvent methanol. 1a,d The reactions of the Dewar pyrimidinones 2 depend strongly upon the substituents at the 1, 3, and 6 positions. 1 The photochemical and thermal reaction scheme of the 2,3,6-trialkyl-4-pyrimidinone 1 and Dewar pyrimidinone 2 .…”
Section: Introductionmentioning
confidence: 95%
“…The photolysis of 2,3,6-trialkyl-4(3 H )-pyrimidinones 1 undergoes a variety of reactions in protic solvents (alcohol, carboxylic acid, amine, and water) .…”
Section: Introductionmentioning
confidence: 99%
“…A good example of the reaction is found with 3- tert -butyl-1,6-dimethyl Dewar isomer 2a in methanol solution. The Dewar isomer gives N -methyl-3-(1-amino-2,2-dimethylpropylidene)-4-methoxy-4-methyl-2-azetidinone ( 3a ) in a quantitative yield (94%) 1f…”
Section: Introductionmentioning
confidence: 99%
“…This indicates that the solvent molecules as nucleophiles attack neither at the imine CN bond nor at the amide NC(O) bond. The initial step in methanol may involve an ionic cleavage of the C1N2(C3) bond by transfer of proton to the N2 atom from the solvent molecules to give an azetidinyl cation, followed by addition of methanol molecule. 1a,h At the present time, we assume that the ionic cleavage in the C1−N2 bond takes place also in carboxylic acid, amine, and water. The C1−N2 bond may be polarized into the cationic carbon (C1 + ) and anionic nitrogen (N2 - ) atoms and is probably lengthened to release the dihydroazete ring strain.…”
The structures of the 5-oxo-2,6-diazabicyclo[2.2.0]hex-2-enes (imine Dewar pyrimidinones) 2a-h have been studied by X-ray diffraction analysis and ab initio calculations at the HF/6-31G(d,p) and MP2/6-31G(d,p) levels of theory. The crystal structures of 1-alkyl-3-tert-butyl-6-methyl imine Dewar pyrimidinones 2a-c have been determined at low temperature. The X-ray diffraction studies revealed that both the 2-azetidinone and dihydroazete rings are almost planar, and their eight bond angles are nearly 90 degrees (81-100 degrees ). The C1-N2(=C3) bond distance in the dihydroazete ring is longer due to the bond angle strain by ca. 0.06 Å than that of a typical straight-chain imine molecule. Full geometry optimizations on the imine Dewar isomers (2a and 2d-h) show deviations between the HF and MP2 geometries. The MP2 structure of the 3-tert-butyl-1,6-dimethyl imine Dewar pyrimidinone 2a is compared with those of the X-ray diffraction. The results of the calculations are found to be in good agreement with the X-ray diffraction data. The full geometry optimizations are necessary with the inclusion of electron correlation for the highly strained molecules. The ab initio calculations of the 2-azetidinone 9, 3,4-dihydroazete 11, and N-ethylidenemethylamine 12 have been carried out at the HF and MP2/6-31G(d,p) levels of theory to compare with the structures, orbital hybridization, bond orders, and charge distributions of the Dewar pyrimidinones 2. The theoretical results reveal that the MP2 C1-N2 bond distance of the Dewar pyrimidinone 2a is consistent with the abnormally elongated X-ray C1-N2 bond distance. The electronegative N2 and N6 atoms in the Dewar pyrimidinones 2 give the great positive charge on the C1 atom. The smaller bond angles (ca. 90 degrees ) in the Dewars 2 than typical sp(2) and sp(3) bond angles (ca. 120 and 109 degrees ) increase p character in the endocyclic bonds and decrease p character in the exocyclic bonds.
“…6- tert -Butyl-2,3-dimethyl-4(3 H )-pyrimidinone ( 1a ), 2-benzyl-6- tert -butyl-3-methyl-4(3 H )-pyrimidinone ( 1b ), and 6- tert -butyl-3-methyl-2-(4-methylbenzyl)-4(3 H )-pyrimidinone ( 1c ) were prepared from iodomethane and 6- tert -butyl-2-methyl-4(3 H )-pyrimidinone, 2-benzyl-6- tert -butyl-4(3 H )-pyrimidinone, and 6- tert -butyl-2-(4-methylbenzyl)-4(3 H )-pyrimidinone in alcoholic solutions containing base at 65−80 °C. The starting 4(3 H )-pyrimidinones were synthesized from the corresponding amidines and β-keto esters. 1f,h …”
Section: Methodsmentioning
confidence: 99%
“…The reactive and unstable photochemical intermediates are the valence-bond isomers (Dewar pyrimidinones) 2 , which react with the protic solvent molecules to give the 4-methoxy-2-azetidinone 3 in methanol, pyrimidinium-5-carboxylate 4 in acetic acid, imine 5 in methylamine, and enamide 6 in water or aqueous solution. However, irradiation of the 3-methyl-, 2,3-dimethyl-, and 3,6-dimethyl-4(3 H )-pyrimidinones in methanol did not give the expected 4-methoxy-2-azetidinone 3 , but, rather, a variety of the degradation products formed by the reactions of the labile imine Dewar pyrimidinones 2 with solvent methanol. 1a,d The reactions of the Dewar pyrimidinones 2 depend strongly upon the substituents at the 1, 3, and 6 positions. 1 The photochemical and thermal reaction scheme of the 2,3,6-trialkyl-4-pyrimidinone 1 and Dewar pyrimidinone 2 .…”
Section: Introductionmentioning
confidence: 95%
“…The photolysis of 2,3,6-trialkyl-4(3 H )-pyrimidinones 1 undergoes a variety of reactions in protic solvents (alcohol, carboxylic acid, amine, and water) .…”
Section: Introductionmentioning
confidence: 99%
“…A good example of the reaction is found with 3- tert -butyl-1,6-dimethyl Dewar isomer 2a in methanol solution. The Dewar isomer gives N -methyl-3-(1-amino-2,2-dimethylpropylidene)-4-methoxy-4-methyl-2-azetidinone ( 3a ) in a quantitative yield (94%) 1f…”
Section: Introductionmentioning
confidence: 99%
“…This indicates that the solvent molecules as nucleophiles attack neither at the imine CN bond nor at the amide NC(O) bond. The initial step in methanol may involve an ionic cleavage of the C1N2(C3) bond by transfer of proton to the N2 atom from the solvent molecules to give an azetidinyl cation, followed by addition of methanol molecule. 1a,h At the present time, we assume that the ionic cleavage in the C1−N2 bond takes place also in carboxylic acid, amine, and water. The C1−N2 bond may be polarized into the cationic carbon (C1 + ) and anionic nitrogen (N2 - ) atoms and is probably lengthened to release the dihydroazete ring strain.…”
The structures of the 5-oxo-2,6-diazabicyclo[2.2.0]hex-2-enes (imine Dewar pyrimidinones) 2a-h have been studied by X-ray diffraction analysis and ab initio calculations at the HF/6-31G(d,p) and MP2/6-31G(d,p) levels of theory. The crystal structures of 1-alkyl-3-tert-butyl-6-methyl imine Dewar pyrimidinones 2a-c have been determined at low temperature. The X-ray diffraction studies revealed that both the 2-azetidinone and dihydroazete rings are almost planar, and their eight bond angles are nearly 90 degrees (81-100 degrees ). The C1-N2(=C3) bond distance in the dihydroazete ring is longer due to the bond angle strain by ca. 0.06 Å than that of a typical straight-chain imine molecule. Full geometry optimizations on the imine Dewar isomers (2a and 2d-h) show deviations between the HF and MP2 geometries. The MP2 structure of the 3-tert-butyl-1,6-dimethyl imine Dewar pyrimidinone 2a is compared with those of the X-ray diffraction. The results of the calculations are found to be in good agreement with the X-ray diffraction data. The full geometry optimizations are necessary with the inclusion of electron correlation for the highly strained molecules. The ab initio calculations of the 2-azetidinone 9, 3,4-dihydroazete 11, and N-ethylidenemethylamine 12 have been carried out at the HF and MP2/6-31G(d,p) levels of theory to compare with the structures, orbital hybridization, bond orders, and charge distributions of the Dewar pyrimidinones 2. The theoretical results reveal that the MP2 C1-N2 bond distance of the Dewar pyrimidinone 2a is consistent with the abnormally elongated X-ray C1-N2 bond distance. The electronegative N2 and N6 atoms in the Dewar pyrimidinones 2 give the great positive charge on the C1 atom. The smaller bond angles (ca. 90 degrees ) in the Dewars 2 than typical sp(2) and sp(3) bond angles (ca. 120 and 109 degrees ) increase p character in the endocyclic bonds and decrease p character in the exocyclic bonds.
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