Otohiko Tsuge

Recent advances in synthetic applications of nitrile oxide cycloaddition (1981-1989)

The synthetic applications of nitrile oxide cycloadditions, developed in the 1980s, are briefly reviewed. Topics discussed in the present review are the modern developments on the generation methods of nitrile oxides, on the cycloadditions with multiple bonds other than carbon-carbon double and triple bonds, on reductive cleavage of the nitrogen-oxygen bonds of 2-isoxazolines, on the unmasking of functionalities, and on the asymmetric cycloadditions of nitrile oxides

Recent Advances in Azomethine Ylide Chemistry

Publisher Summary Azomethine ylides are planar molecules composed of one nitrogen and two terminal sp2 carbons. At most, four geometrical isomers are possible for these transient molecules. Their cycloadditions to olefin or acetylene dipolarophiles give rise to the formation of two sets of carbon-carbon bonds in a single step. Because of the structural complexity of azomethine ylide itself compared to other dipoles and the stereochemical selectivity in the cycloadditions, a number of stereoisomers are possible for the cycloadducts. These two points make azomethine ylides one of the most attractive 1,3-dipoles, both in the fields of ylide chemistry and synthetic organic chemistry. Azomethine ylides can be classified in groups according to their structure. This chapter concentrates on the most basic ylides, acyclic azomethine ylides, in order to catch the generalized concepts involved in the azomethine ylide chemistry. Accordingly, it also deals with the recent advances of the chemistry of acyclic azomethine ylides covering its preparation, cycloadditions, intramolecular cycloadditions, and synthetic applications.

Photochemistry of heterocyclic compounds—II : The photochemical reaction of 2,5-disubstituted 1,3,4-oxadiazoles with furan

Abstract The photochemical reaction of 2,5-disubstituted 1,3,4-oxadiazoles with furan has been studied. With or without benzophenone as a sensitizer, irradiation of 2,5-diphenyl-1,3,4-oxadiazole with furan in benzene solution gives the 1 : 1 cycloadduct, tetrahydrofuro[2·3-b]azetidino[2·1-b]-1,3,4-oxadiazole. However in the presence of iodine 3-acylfurans and their acylhydrazones are formed. A reaction pathway of this novel photo-induced acylation has been suggested.

Studies of thiobenzoyl isocyanate—I : Reaction of thiobenzoyl isocyanate with hydrazines☆

Abstract The reaction of thiobenzoyl isocyanate with hydrazines is reported. With hydrazine hydrate, 4 H -5-phenyl-1,2,4-triazole-3(2 H )-one was obtained in a good yield. In the reaction with mono-substituted phenylhydrazines, 2,3-dihydro-2-aryl-5-phenyl-1,2,4-triazole-3(1 H )-one or 3-hydroxy-1-aryl-5-phenyl-1,2,4-triazole, or both were formed: the relative amount of the triazoles depended on the nature of the substituents. The reaction with 2,4-dinitrophenylhydrazine, however, gave the semicarbazide which, when treated with aqueous sodium hydroxide or polysphosphoric acid, suffered no ring closure to the triazole. Benzoyl isocyanate reacted with benzylhydrazine, yielding the same triazolone as that obtained from the reaction of thiobenzoyl isocyanate with the hydrazine. The products from these reactions have been identified by independent synthesis as well as IR and UV spectra.

Studies of acyl and thioacyl isocyanates—XII : The reactions of benzoyl and thiobenzoyl isocyanates with sulfonium ylides and with diazoalkanes

Abstract Benzoyl isocyanates react with ethyl (dimethylsulfuranilidene) acetate, dimethyl sulfonium phenacylide and dimethyloxosulfonium methylide to give the corresponding stable benzoylcarbamoyl- sulfonium ylides which on pyrolysis, are converted into oxazoles. However, with dimethylsulfonium phenacylide, thioacyl isocyanate affords the thiazole derivative. In connection with the formation of oxazoles, the reaction of benzoyl isocyanates with some diazoalkanes was also investigated: the products are not 1,2,3-triazolones as reported by Neidlein, but instead benzoylcarbamoyldiazo compounds which were thermally decomposed to oxazoles.

Studies of acyl isocyanate—IV : Synthesis of dioyl diisocyanates☆☆☆

Abstract An attempt has been made to prepare aliphatic and aromatic dioyl diisocyanates according to Speziales method. The reactions of sebac-, phthal-, isophthal- and terephthalamide with oxalyl chloride progressed smoothly, forming the corresponding isocyanate, which in turn gave quantitatively the corresponding bifunctional acylurea on treatment with aniline in all cases except phthaloyl isocyanate. In the reaction of succin- or adipamide, however, the amide required a large amount of oxalyl chloride, and in addition to the expected isocyanate, 1,2-bis[2-(1,3-oxazolidine-4,5-dione)] ethanediylidene or 1,3-adipoylimidazoline-2,4,5-trione was obtained. The hydrazinolysis and anilinolysis of the above by-products are also presented.

Studies of acyl and thioacyl isocyanates—XI : The reactions of benzoyl and thiobenzoyl isocyanates with 2-thiazolines and 2-oxazolines☆

Abstract Thiobenzoyl isocyanate adds to 2-thiazoline and its 2-methyl derivative to afford the corresponding (4 + 2) cycloadducts. Reaction of benzoyl isocyanate with 2-methylthiazoline gives 2,3-dihydro-5-phenyl-8-benzoylcarbamoylthiazolo[3,2-c]pyrimidin-7-one. Thiobenzoyl isocyanate reacts with 2-methyl-2-thiazoline and -2-oxazoline at 90° to form the corresponding 8-thiobenzoylcarbamoylthiazolo- and -oxazolo[3,2-c]pyrimidin-7-ones, while reaction of benzoyl isocyanate with 2-methyloxazoline affords a 2:1 adduct, which with acetic acid gives the corresponding oxazolo[3,2-c]pyrimidine. Benzoyl isocyanate reacts with 2-ethyl-2-thiazoline to afford 2,3-dihydro-6-benzoyl-8-methylthiazolo[3,2-c]pyrimidine-5,7-dione and 2,3-dihydro-5-phenyl-8-methylthiazolo[3,2-c]pyrimidin-7-one; their acid and alkaline hydrolyses are described. Formation of these products is shown to proceed via attack of both isocyanates on the β-carbon of the tautomeric enamines of 2-alkyl-2-thiazoline and -2-oxazoline.

Ring closure reactions of adducts of methacryloyl isocyanate to arylhydrazines and their related compounds

Methacryloyl isocyanate (MAI) reacted with arylhydrazines (1) to give semicarbazides (2) in good yields. Treatment of (2) with aqueous potassium hydroxide gave the corresponding 1-aryl-3-hydroxy- 1,2,4-triazoles (3), whereas thermal ring closure of (2) afforded isomeric 2,3-dihydro-2-aryl-1,2,4-triazole-3(1H)-ones (4). MAI reacted with benzamidine to give directly 1,3,5-triazine-2(1H)-one (10) by the loss of water. On the other hand, the reaction of MAI with 1,3-diphenyl- guanidine afforded the 1:1 adduct (11), which on thermal decomposition gave the perhydropyrimidin-6(1H)-one (12) and perhydro-1,3,5-triazine- 2,6-dione (13). The pathways for the formation of (4), (12) and (13) are also described

Studies of acenaphthene derivatives—XXVIII : The reaction of 2-diazoacenaphthenone with anils in the presence of boron trifluoride

Abstract Reaction of 2-diazoacenaphthenone with anils in the presence of a catalytic amount of boron trifluoride etherate is reported. The diazoketone reacts with benzylidenanilines to afford a mixture of stereoisomers of spiro[acenaphthenone-2′,4-imidazolidine], whose structures correspond to compounds derived from 1:2 adducts of the diazoketone and anils with the elimination of nitrogen. A pathway involving spiro-aziridine intermediates is proposed for their formation. Reaction of the diazoketone with aα-alkylbenzylidenanilines however gives the corresponding acenaphtho[1,2-b]pyrroles, whose structures correspond to compounds arising from 1:1 adducts with the elimination of both nitrogen and water. The reaction of the tautomeric enamine form of the anil with a carbenoid intermediate generated from the diazoketone is suggested for pyrrole formation.