Quinazolines ring-cleavage

Substituted quinazolin-4(3//)-ones, unavailable by other known routes, are obtained via ring cleavage and subsequent intramolecular cyclization of enamino ketones 31. ... 

Alkyl-2-phenylquinazolines 9 are readily available by reaction of 5,S -dimethyl-A-(A-aryl-benzimidoyl)sulfimides 7 with enamines 8 in refluxing Tetralin (1,2,3,4-tetrahydronaphthalene). The mechanism of quinazoline ring formation probably involves a thermal cleavage of the imidoylsulfimides into imidoyl nitrenes, nitrene addition to the enamine double bond and subsequent rearrangement of the aziridine intermediate thus formed to the final product 9. Small amounts (10-15%) of 4-unsubstituted quinazolines 10 are obtained as byproducts. The formation of these byproducts involves a known intramolecular rearrangement of the benz-imidoylsulfimides employed. ... 

Prolonged reduction of quinazoline, 2-chloroquinazoline, 4-chloroquinazoline, and 4-phenyl-sulfanylquinazoline with lithium aluminum hydride results in ring cleavage and formation of diamines 2 in addition to the partially reduced quinazolines. ... 

In a similar fashion, quinazolin-4-ones 72 were synthe.sized by reactions of 70 with anthranilate 71 in presence of molecular sieves as reported by Tatibouct and co-workets <01TL2977>. Ring cleavage took place under either basic or acidic conditions to give quinazolin-2,4-diones 73. 

The 1,3-diazines have also been prepared by a reaction of enamines and S, S -dimethyl-A (A arylbenzimidoyl)sulfimides 360 in boiling tetraline220,221. The mechanism of the ring formation probably involves a thermal cleavage of the imidoylsulfimides 360 into imidoylnitrenes 361 and dimethyl sulfide. The nitrene can then react with the enamine to give an aziridine intermediate 362 which rearranges to a 3,4-dihydroquinazoline 363. Subsequent elimination of amine yields the quinazoline 364220. 

Reaction of N-(2-chloroacetyl)anthranilic acid (386) with thiourea in ethanol at reflux temperature gives 2fl -thiazolo[3,2-a]quinazolin-l,5-dione (336) via intermediates 387 and 388 (not isolated) as formulated in Scheme 88 (69IJC881). Unlike the case of 384, the thiazolidinone ring in 336 did not undergo cleavage because the reaction medium was not alkaline (Scheme 89),... 

Quinazolin-4(3//)-ones are not readily degraded by reagents in alkaline media because they form stable anions. However, if the tautomeric hydrogen is substituted, then the heterocyclic ring becomes susceptible to cleavage. Two such examples are 3-propadienylquinazolin-4-one (33) and l-acetyl-2-(a-ethoxy-a-phenyl)benzylquinazolin-4-one (34). When the former compound was boiled for 2 hours with sodium in 96% ethanol, nucleophilic attack at C-2 occurred and 2-(2-formamidophenyl)-5-methyloxazole was formed by a subsequent reaction of the olefinic side chain. The second... 

In contrast, UV irradiation of llfi, which retains the double bond between C5 and C6, resulted in the cleavage of the cyclobutene ring to produce propyne and quinazoline (23fi) in place of the anticipated pentacyclododecane (22fi) (Scheme 20). These findings indicate that the removal of the C5-C6 double bond may be essential for the formation of pentacyclo[6.4.0.0 .0 0 ]dodecanes. 

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