Yukio Ikemi

Reaction of 3-aroylaziridines with diphenylcyclopropenone and subsequent stereospecific 1,3-dipolar cycloaddition of the adducts with dimethyl 1-cyclobutene 1,2-dicarboxylate

Reaction of 3-aroylaziridines with diphenylcyclopropenone provides anhydro-3-hydroxy-2,4-diphenyl-6-arylpyrylium hydroxides that undergo stereospecific 1,3-dipolar cycloaddition with dimethyl 1-cyclobutene 1,2-dicarboxylate to give the corresponding exo- and endo-adducts depending on the substitutents of the 6-phenyl group.

Hilbert-johnson reaction under high pressure : A facile preparation of 2-pyridones

For the first time, a facile synthesis of 2-pyridones utilizing a classical Hilbert-Johnson reaction of 2-methoxypyridines with haloalkanes under high pressure has been achieved. The reactions were sensitive to steric hindrance of haloalkanes.

Reactions of 5-Cyano-1,4-diphenylpyridazino[4,5-a]indolizines with Dimethyl Acetylenedicarboxylate: Regioselective Formation of 1:2 Michael Type Adducts

Reactions of 5-cyano-1,4-diphenylpyridazino[4,5-a]indolizines with dimethyl acetylenedicarboxylate afforded regioselectively the 1:2 adducts in a Michael fashion rather than in a 1,3-dipolar manner. The structure was established by an X-ray crystallography

INVERSE ELECTRON DEMAND DIELS-ALDER REACTIONS OF 3, 6-DIARYL-1, 2, 4. 5-TETRAZINES WITH CYCLOOCTYNE

Cyclooctyne 2 underwent inverse electron demand Diels-Alder reaction with a variety of 3,6-diaryl-l, 2, 4, 5-tetrazines 1 , giving the corresponding pyridazines 3 in excellent yields. LUMO 1 -HOMO 2 energy gaps between 1 and 2 are obtained by semi-empirical molecular orbital calculations. Cyclooctyne is the smallest cyclic alkyne that is stable at room temperature and has been prepared by a number of methods which either start from cyclooctene or from cyclooctanone.1 In spite of high strain and high reactivity of cyclooctyne as well as synthetic potential of its cycloadditions, relatively few examples of cycloaddition reactions have been reported.2 1, 2. 4, 5-Tetrazines aire well known to act as electron deficient dienes in inverse electron demand Diels-Alder reactions, providing access to highly functionalized pyridazines.3·4 The ab initio quantum-mechanical and experimental mechanistic stüdies of this reaction also have been reported.5 Since only one isolated example of Diels-Alder reaction of the bis-1, 2, 4, 5-tetrazine with cyclooctyne is reported ,6 it would be desirable to describe more detailed and systematic studies of the reactions. For example, the reaction of 3,6-bis(4-methoxyphenyl)-1,2,4,5-tetrazine l a with 2.7 molar amount of cyclooctyne 2 in refluxing toluene for 1 h gave l,4-bis(4-methoxyphenyl) cyclooctano[4,10-a]pyridazine 3a in 77 % isolated yield. The reaction is believed to proceed via the 1:1 adduct 4, followed by elimination of nitrogen, giving the corresponding pyridazines. The mechanism has been recently theoretically proven by ab initio calculations.5 The generality of the reaction with cyclooctyne has been confirmed as summarized in Table 1. The I3C NMR spectra of 3 have established their symmetrical structure (see, experimental), while 1,4-aromatic rings often showed either slightly different ]H NMR signals like 3a or complex signals like 3k, presumably because of their slow rotation. Vol. 5, No. 1, 1999 Inverse electron demand Diels-Alder reactions of 3,6-diaryl-l,2,4,5-tetrazines with cyclooctyne Table 1. Diels-Alder Reactions of 3, 6-Diaiyl-l. 2, 4. 5-tetrazines l_wlth Cyclooctyne 2 Molar Ratio Reaction ( 1 : 2 ) Time ( h ) Yield ( % ) l a 4-MeOC6H4 1 : 2.7 1 3a 77 l b 2-Pyridinyl 1 : 1.3 1 3b 89 lc 3-Pyridinyl 1 : 1.3 1 3c 93 Id 4-Pyridinyi 1 : 1.3 1 3d 86 l e Ph 1 : 2 2 3e 93 If 3-MeC6H4 1 : 1.3 2 3f 92 U 4-MeC6H4 1 : 2 1 3g 96 l h 3-FCqH4 1 : 1.3 2 3h 93 l i 4-FCgH4 1 : 1.3 0.5 3i 90 U 3-ClC6H4 1 : 1.3 2 3i 99 l k 4-ClC6H4 1 : 1.3 2 3k 91 11 3-BrC6H4 1 : 1.3 1 31 89 l m 4-BrC6H4 1 : 1.3 1 3m 81 Table 2. HOMO-LUMO Energy Gaps Between 1 and 2 Calculated by PM3. Ar HOMO(eV) LUMO(eV) HOMO 1-LUMO 2 LUMO 1-HOMO 2 l a -8.844 -1.621 10.413 8.541 l b -9.669 -1.883 11.238 8.279 l c -9.715 -2.071 11.284 8.091 Id -10.053 -2.198 11.622 7.964 l e -9.335 -1.745 10.904 8.417 If -9.334 -1.746 11.903 8.416 l i -9.106 -1.687 10.675 8.475 l h -9.657 -2.046 11.226 8.116 l i -9.479 -2.007 11.048 8.155 11 -9.438 -1.920 11.007 8.242 lk -9.212 -1.941 10.781 8.221 11 -9.538 -1.985 11.107 8.177 l m -9.518 -2.013 11.087 8.149

Site selectivity in the 1,3-dipolar cycloaddition reaction of unsymmetric pyridinium bis(methoxycarbonyl)methylides with methyl propiolate

The 1,3-dipolar cycloaddition of unsymmetric pyridinium bis(methoxycarbonyl)methylides with methyl propiolate proceeds in moderate to good yields with high to moderate site selectivity with respect to the ylide. Polar 3-substituted pyridinium bis(methoxycarbonyl)methylides generally gave predominantly the corresponding 8-substituted indolizines regardless of the substituents. The results can be explained by dipole-dipole interactions

A FACILE AND SOLVENT-FREE SYNTHESIS OF 3,5 -DISUBSTITUTED-4-AMINO-1,2,4-TRIAZOLES BY REACTIONS OF AROMATIC NITRILES WITH HYDRAZINE

A variety of 3, 5-disubstituted-4-amino-l,2,4-triazoles were prepared by reactions of aromatic nitriles with hydrazine monohydrate. The structure of 3.5-diphenyl-4-amino-l ,2,4-triazoIe was established by an X-ray analysis. 4-Amino-1,2,4-triazoles derivatives have rather Interesting activities such as fungicides (la-c), herbicides and pesticides (2), and more recently, have been used as organic electroluminescent material and devices (Id). 4-Amino-1,2.4-triazoles have been prepared by a number of methods (2). Previously, we reported preparation of a variety of 3,6-diaryl-l, 2, 4, 5-tetrazines and their inverse electron demand Diels-Alder reaction with cyclooctyne (3). During the course of preparation of a variety of 3,6-diaryl-l, 2, 4, 5-tetrazines from aromatic nitriles and hydrazine, we obtained colorless solids when a mixture of these was vigorously refluxed (4). Fortunately, one of the compounds formed a single crystal which was subjected to an X-ray analysis and was unambiguously proven to be 3,5-diphenyl-4-amino-l,2,4-triazole (5). Therefore, we describe below briefly a facile and solvent-free synthesis of 3,5-disubstituted-4-amino-l,2,4-triazoles 3 by reactions of aromatic nitriles 1 with hydrazine monohydrate 2. The reaction procedure is extremely simple: for example, a mixture of benzonirile Jla (4.95g. 0.048 mol) with hydrazine monohydrate 2 (14.447g, 0.288 mol) was refluxed for 48 h. The colorless precipitates were separated by filtration which were dried under vacuum giving crude 3.5-diphenyl-4-amino-l,2,4triazole 3a in 74 % yield (4.2 g) (6). The analytically pure sample was obtained by recrystallizing from ethanol.

Comparative X-ray Diffraction Studies and Molecular Orbital Calculations on Diazinium Dicyanomethylides

Abstract Comparative studies have been described between X-ray analyses (1a: Pnma (No. 62), a = 9.069(4) Å, b = 6.411(4) Å, c = 12.299(3) Å, U = 715.1(5) Å3, Z = 4, DC = 1.3339 gcm−3, R = 0.052, and Rw , = 0.066 for 599 independent observed reflections. 1b: P21/m (No. 11), a = 3.824(5) Å, b = 12.593(3) Å, c = 6.685(3) Å, = 91.80(6)°, U = 321.8(4) Å3, Z = 2, DC = 1.487 gcm−3, R = 0.052, and Rw = 0.063 for 599 independent observed reflections) and molecular orbital calculations of pyridazinium (1a) and pyrazinium (1b) dicyanomethylides. Generally, ab initio calculations reproduce the geometry better than semi-empirical methods.

Reaction of 3-aroylaziridines with diphenylcyclopropenone. 1,3-Dipole cascade from azomethine ylide to carbonyl ylide

Abstract The novel formation of anhydro -3-hydroxy-2,4-diphenyl-6-arylpyrylium hydroxide in the reaction of 3-aroylaziridines with diphenylcyclopropenones and their 1,3-dipolar cycloaddition reactions with diphenylcyclopropenone, N-phenylmaleimide, dimethyl fumarate, and dimethyl maleate were described.

MOLECULAR INCLUSION CRYSTALS OF NOVEL HETEROCYCLIC HOST COMPOUNDS

Abstract Inclusion phenomena of the solvents such as hexane, benzene, and dichloromethane in either the crystals or glassy states of the armed-1,4,8,12-tetrazacyclopentadecanes were observed, whereas only few inclusion was found in the armed 1,4,8,11- tetraazacyclotetradecanes. As further examples of undesigned inclusion hosts, the 1:2 adduct, obtained by Diels-Alder reaction of [2.2]paracyclophane with 4-phenyl-1,2,4-triazoline-3,5-dione, along with the 1:2 adducts fiom 5-cyano- 1,4-diphenylpyridazino[4.5-a]- indolizines and dimethyl acetylenedicarboxylate (DMAD) are described.