3.1- Benzoxazine-2,4-diones

Only two articles deal with the synthesis of saturated 1,3-benzoxazine-2,4-diones and the corresponding cyclopent[e][l,3]oxazines. 

Another example of ring enlargement is provided by the aminomethylation of the potassium salt of N-hydroxy-phthalimide (Fig. 70), whieh affords the Mannich base 198 of dihydro-benzoxazine-dione, instead of the O-Mannich base of N-hydroxy-phthalimide, as previously proposed. -... 

Pyrano[3,2-c]benzopyran-2,5-diones synthesis, 3, 808 Pyranobenzopyranones crystal structures, 3, 623 Py rano[3,2-c][ 1 ]benzopyran-2-ones synthesis, 3, 797 Pyranobenzothiazoles mass spectra, 3, 615 Pyrano[2,3-y]benzoxazine synthesis, 3, 714... 

Four-membered heterocycles are easily formed via [2-I-2] cycloaddition reac tions [65] These cycloaddmon reactions normally represent multistep processes with dipolar or biradical intermediates The fact that heterocumulenes, like isocyanates, react with electron-deficient C=X systems is well-known [116] Via this route, (1 lactones are formed on addition of ketene derivatives to hexafluoroacetone [117, 118] The presence of a trifluoromethyl group adjacent to the C=N bond in quinoxalines, 1,4-benzoxazin-2-ones, l,2,4-triazm-5-ones, and l,2,4-tnazin-3,5-diones accelerates [2-I-2] photocycloaddition processes with ketenes and allenes [106] to yield the corresponding azetidine derivatives Starting from olefins, fluonnaied oxetanes are formed thermally and photochemically [119, 120] The reaction of 5//-l,2-azaphospholes with fluonnated ketones leads to [2-i-2j cycloadducts [121] (equation 27)... 

The solid state structure of (3>S,8 Sj-10-(8-amino-6-azaspiro[3,4]octan-6-yl)-9-fluoro-3-methyl-7-oxo-2,3-dihydro-7//-pyrido[l,2,3-dfe]-l,4-benzoxa-zine-6-carboxylic acid (218) was determined by X-ray diffraction study (98CPB1710). The structure of 6,10-dihydropyrido[2,l-c][l,4]benzoxazine-6,10-dione 219 was established by X-ray diffraction analysis. It contains a crystal solvate with /j-xylene (99MI40). 

Under different reaction conditions, however, a 3-hydroxy-l,3-benzoxazin-2,4-dione is formed[122] (see also six-membered heterocycles containing an N—CO—O unit, Section 7.1.6) ... 

Thermal decomposition of l,2-dihydro-477-pyrrolo[2,l-r-][l,4]benzoxazine-l,2,4-triones 425 yielded 7-(2,4,6-trimethylbenzoyl)-8-[(2,4,6-trimethylphenoxycarbonyl)-6,10-dihydropyrido[2,l-r-][l,4]benzoxazine-6,10-dione by [4+2] cycloaddition of the initially formed ketene 426 and the subsequent rearrangement of 6,8,9,10-tetrahydropyrido[2,l-c][l,4]benzoxazine-6,8,10-trione 427 (Scheme 36) <1999RCB2131>. 

The 2,3-dihydro-5//,7//-[l,4]oxazino[2,3,4-i,/)[3,l]benzoxazine-5,7-dione 390 suffered ring opening and decarboxylation to the dihydro-[l,4]-benzoxazine-5-carboxylate 391 on treatment with sodium ethoxide (Equation 43) <1997FRP2759699>. 

H-1,3-Benzoxazine-2,4(3H)-dione (7.98) is an interesting cyclic carbamate. Hydrolysis of the ester group likely yields the ring-opened carbamic acid 7.99 as an undetected intermediate, which very rapidly decarboxylates to form the product salicylamide (7.100). When the cyclic carbamate was ad-... 

Another method was developed for the synthesis of 5,8-methano-3,l-benzoxazine-2,4-diones 157. The A-BOC amino acid 156 was prepared from the half ester 155 without purification of the intermediates. Thus, 155 was treated with ethyl chloroformate, and subsequently with sodium azide. 

The constitutionally isomeric 3-substituted (l//,3//)-quinazoline-2,4-diones and 2-phenylimino-4//-3,l-benzoxazin-4-ones are easy to distinguish via their El mass spectra (93RCM374). For quinazolinediones, the most striking feature is the loss of CO2, proving that a rearrangement due to anilino migration must occur. 

When the N -2-(hydroxymethyl)cyclohexyluracil 450 was treated with AT-chlorosuccinimide in DMF at room temperature, ring closure again occurred to give a mixture of monochloro- (5%) and dichloro- (92%) hexahydropyr-imido[l,6 7][3,l]benzoxazin-l,3-diones 451 and 452 <2006T9949>. 

The wide range of chemical transformations to which 2//-3,l-benzoxazine-2,4-dione (isatoic anhydride) 4 has been subjected is beyond the scope of this chapter. A review published a few years ago on the transformations of isatoic anhydrides to heterocyclic compounds contains valuable information on other aspects of the chemical behavior of these compounds <2001CHE385>. 

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