1.3- Oxazinium perchlorates

Ethyl 2,4,7-triaryl-l,3-oxazepine-6-carboxylates 15 are formed in modest yield by the reaction of ethyl diazoacetate with 1,3-oxazinium perchlorates 14.13... 

Monocyclic 1,3-oxazepines (325) with aryl substituents at the 2-, 4- and 7-positions can be prepared in moderate yield (20-40%) by the reaction of aliphatic diazo compounds with 1,3-oxazinium perchlorates (324) (74S187). Tetra- and penta-phenyl-l,3-oxazepines (328 R = H or Ph) have been obtained via the reaction of azide with pyrylium salts (326) (78H(l 1)331). This principle had earlier been applied to the preparation of 1,3-benzoxazepines (74CR(C)(278)1389> and more recently to 3,1-benzoxazepines (81JHC847). The preparation of 2-phenyl-1,3-oxazepine.(331) by the UV irradiation of (329) is mechanistically interesting in that it apparently involves an intermediate (330) of the same type as (327) (73TL1835), but the method has only been used in this one case. One of the few examples of a dihydro-1,3-oxazepine (333) has been prepared by the thermolysis of the aziridine (332) (68JOC4547). 

Oxazinium perchlorates (267) are obtained by reactions of 1,3-diketones and benzonitrile in the presence of perchloric acid and acetic anhydride (88ZOR1561, 88ZOR2232, 91ZOR1986). 1,3-Thiazinium perchlorates are synthesized by treating oxazinium salts with hydrogen sulfide in absolute acetonitrile and then with perchloric acid (72S333). 

Monocyclic 1,3-oxazepines 419 can be prepared by reaction of aliphatic diazo compounds with 1,3-oxazinium perchlorates 418 (Scheme 194) <1974S187>. Tetra- and penta-phenyl-1,3-oxazepines 421 (R = H or Ph) have been obtained by the reaction of azide ion with pyrylium salts 420 (Scheme 195) <1978H(11)331>. 

When 1,3-oxazinium perchlorates (210) were heated in DMF in the presence of AC2O, pyrido[l,2-c]pyrimidinium perchlorates (211) were formed (91KGS1556). 

A stirred solution of 2,4,6-triphenyl-l,3-oxazinium perchlorate (3.06 g, 7.5mmol) in MeCN (100 mL) was treated with ethyl diazoacetate (1.80 mL, 17.2 mmol) followed by i-Pr2NEt (0.64 mL, 3.75 mmol). After ca. 30 min the theoretical amount of N2 had been evolved. The solution was stirred for 15 h, aq NaHC03 was added and the mixture was extracted with CHC13. The dried (K2C03) extract was concentrated and the residue was chromatographed (silica gel, benzene) yield 1.10 g (38%) mp 161 C. 

The rate of alkaline hydrolysis of 3,4,6,7,8,9-hexahydro-2H-pyrido-[2,l-h]oxazinium perchlorates to the thermodynamic l-(3-hydroxypropyl)-... 

The bicyclic lactam acetal (40) was formed when pyrido[2,l-b][l,3]-oxazinium perchlorate (38) was treated with sodium methylate [70JCS(CC)900]. Treatment of 38 with sodium alcoholate and then with an alkyl halide gave quaternary salts 35, presumably as a mixtures of two stereoisomers (79TL809). 

By acylation of the enol form 85 of / -ketonitriles 84,4-oxo-l,3-oxazinium perchlorates 86 are obtained. Opening the cycle by hydrolysis to give 87 occurs under mild conditions70 (equation 31). 

The only known fully unsaturated 1,3-thiazepines are ethyl 2,4,7-triaryl-l,3-thiazepine-6-car-boxylates 2, which are formed in moderate yield by the action of ethyl diazoacetate on 2,4,6-triaryl-l,3-thiazinium perchlorates 1 in a reaction analogous to that of oxazinium salts the preparative procedure is analogous to that given for ethyl 2,4,7-triaryl-l,3-oxazepine-6-car-boxylates (see Section 4.1.1.2.1.1.).13... 

A-Acyl-jS-enamino ketones (306), prepared from A-substituted dithiocarbonimidates and the potassium enolates of methyl ketones, on treatment with perchloric acid or methanesulfonic acid, yield 1,3-oxazinium salts (307) (Equation (30)) <83JOC623>. 

Diamino-1,3-thiazinium salts (179) are obtained in a similar way from 2-acyl-1-chloro-enamines (180) and thioureas in the presence of either perchloric or tetrafluoroboric acid (X = CIO4 or BF4), but if the enamines (180) are reacted with thiobenzamide the products are 4-amino-1,3-oxazinium salts (181) (Scheme 33) <87M1383>. 

N-Acyl-B-enaminoketones (328), readily prepared from the potassium enolates of methyl ketones and diethyl N-(acyl)dithio-carbonimidates (327), are converted into 1,3-oxazinium salts (329) on treatment with 70% perchloric acid in acetic anhydride. The conversion of the 1,3-oxazinium salts to the corresponding... 

Further studies by Soviet workers on the synthesis and reactions of 4-oxo-1,3-oxazinium salts (317) have appeared. The perchlorate salts are available in... 

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