1.3.5- Oxadiazinium salts reactions

Triaryl-l,3,5-oxadiazinium salts 1 are obtained as yellow or reddish pentachlorostannates by the reaction of aroyl chlorides with two equivalents of aromatic cyanides in the presence of tin(IV) chloride.57... 

Aryl cyanates react with aromatic acid chlorides in the presence of anlimony(V) chloride to give 2-aryl-4,6-bis(aryloxy)oxadiazinium salts 5a, b 62 thiocyanates react analogously giving 5c-n but in this case the reaction is of wider scope as both the thiocyanates and the acid chlorides may be aromatic or aliphatic.63,64... 

In an extension of the reaction described, 2,4-bis(dialkylamino)-6-(aminomethyleneamino)-oxadiazinium salts 8 can be synthesized from amino-substituted l-oxa-3-azabutatrienylium hexachloroantimonates and dialkylcyanamides.66... 

The reaction of dicarboxylic acid dichlorides with aryl cyanides in the presence of antimony(V) chloride gives his(1,3,5-oxadiazinium) salts 9a-l whose colors range from yellow to brown.67 The stability of the salts increases with the distance of the heterocyclic rings from each other. 

The more interesting reactions of 1,3,5-oxadiazinium salts with nucleophiles result in the formation of heterocyclic compounds. The nucleophile attacks C2 of the oxadiazinium ring ring opening and recyclization follow. Thus concentrated aqueous ammonia affords 1,3,5-tri-azines I.57... 

Aryl-4,6-bis(methylsulfanyl)-l,3,5-oxadiazinium salts, e.g. 28, obtained by the reaction of thiocyanates and acyl chlorides (cf. Section B.1.3.) react with arylcarboximidamides in dioxane at room temperature to form diaryl-1,3,5-triazines in moderate yield (23 -29%).436... 

Ammonolysis of 1,3,5-oxadiazinium salts gives 1,3,5-triazines. Stable oxadiazinium salts can be formed by reaction of an aryl nitrile with an aromatic acid chloride and Lewis acid (AICI3, SbCls, FeCls, or SnCl4). Electron-withdrawing groups in the aromatic rings render the salts unstable, and they are difficult to isolate. The salts (221) were isolated and converted with ammonia into the triazines (222) (Scheme 68) <86MI 6l2-02>. 

Trimerization of nitriles, isocyanates, isothiocyanates, imidates, and carbodiimides all lead to symmetrical 2,4,6-trisubstituted 1,3,5-triazines (see Section 6.12.9.5). The use of lanthanide trifluoromethanesulfonate and ammonia as cocatalysts is claimed as a big improvement. The trisaminal of 2,4,6-triformyl-l,3,5-triazine is also useful for further derivatization to unusual structures (see Section 6.12.7.1). Treatment of a 1 1 pyridine/conc. ammonia solution of an aromatic aldehyde with excess Fremy s salt is another development. Separation of the amide coproduct was claimed to be easy. The synthesis fails with aliphatic aldehydes (see Section 6.12.9.5.4). Aminolysis of 2,4,6-triaryl-1,3,5-oxadiazinium salts gives symmetrical 1,3,5-triazines but the reactions are limited in that electron-withdrawing groups in the aromatic rings lead to instability and difficulty in separation of products (see Section 6.12.10.4). 

The reactions of oxadiazinium salts (44) with ethanolic ammonia, however, are more complex and yield mixtures of the 1,3,5-triazines (50) and (51). The former, which are minor products (10-... 

Equally complex are the reactions of the oxadiazinium salts (44) with hydrogen sulfide, to yield 3//-l,2,4-dithiazolidines (52) (Scheme 3) <85LA1874>. 

The 4,6-bis(dialkylamino)-l,3,5-oxadiazinium salts (58) undergo a more simple reaction with HjS than that noted for the 4,6-bis(methylthio)-derivatives (53 Scheme 4) in that A-(thioacyl)guanidines... 

Great interest has been shown in the synthesis of 1,3,5-oxadiazinium salts (209) by the reaction of an aryl carbonitrile (2 equivs.) with an acyl halide (1 equiv.) in the presence of a Lewis acid, generally antimony pentachloride (Scheme 32). Stannic chloride, aluminum chloride and ferric chloride have also been employed but are less effective catalysts <1892CB2266, 56CB209, 65CB334, 67CB3736, 86MI 618-01>. 

In a reaction similar to that described for the preparation of 1,3,5-oxadiazinium salts (209) (Scheme 32 see Section 6.18.10.3.1.i) methyl thiocyanate in the presence of SbCh undergoes cyclocondensations with arylthiocarbonyl chlorides to give 2-aryl-4,6-bis(methylthio)-l,3,5-thia-diazinium hexachloroantimonates (221) (39 6%) <88LA729>. 

Antimony pentachloride reacts with a-chloro isocyanates to form l-oxa-3-azabutatriene salts, R2C=N+=C=0 SbCle, 26, which undergo [2+2+2] cycloaddition reactions with disubstituted cyanamides to give 1,3,5-oxadiazinium salts 27. ... 

With the help of a combination of selective dissolution and chromatographic separation, several of the cyclic ethers have been separated and isolated <2003OL3745>. Though not of synthetic value, gas-phase cyclization reactions of acylium ions with nitriles, forming 1,3,5-oxadiazinium ions 375 by double nitrile addition followed by cyclization, have been reported (Scheme 75) <2001MI445>. Similarly, the gas-phase reactions of acylium and thioacylium ions with isocyanates (18 Y = 0) and isothiocyanates (18 Y = S) have been reported to result in oxadiazinium (16 X = 0) and thiadiazinium (16 X = S) salts, respectively (see Scheme 2) <2005JAM1602>. 

---