Furo oxazin-4-ones

The fluoro substituents proved to induce changes in the reactivities of the methyl- (X = H) and trifluoromethyl-substituted (X = F) pyrido[3, 2 4,5]furo[3,2- [l,3]oxazin-4(47r)-ones 105 with nucleophiles. When methyl-substituted compounds 105 (X = H) were reacted with piperidine in toluene, Wacetylamino carboxamides 106 were formed by nucleophilic attack at the carbonyl group of the l,3-oxazin-4-one ring (Scheme 16). However, the similar reactions of the trifluoromethyl-substituted analogs 105 (X = F) resulted in formation of amidino carboxylic acids 107 by attack at electron-poor position 2 <1995JFC(74)1>. 

The synthesis of heterocycles via rDA processes includes the preparation of heterocycles with two different heteroatoms. Furo[3,4-c]pyridine (218), a previously unknown polyheterocyclic, has beat achieved by FVP of adduct (217) (equation 98). The heteropentalene Aieno[3,4-6]fuian (220) has been synthesized by a reaction pathway based upon rDA formation of polyheterocycle (219) (equation 99). Other heterocycles prepared via rDA reactions that contain two differoit heteroatoms include 6H-l,3-oxazin-6-one (221) and 3-arylisoxazoles (222). ... 

Zhang reported a Au(I)-catalyzed diastereo- and enantioselective domino cycHzation/[3+3] cycloaddition of 2-(l-aIkynyl)-2-alken-l-one 216 with nitrone 217, affording the corresponding chiral heterobicyclic furo[3,4-d][l,2]oxazine 218 [67]. This reaction is attractive by its easy scale-up possibility (gram scale) and the chemoselective functional group transformation in the product (Scheme 11.46). 

NHC-catalysedreactions of nitrosoarenes with4-(2-aroylvinyl)furan-3-carbaldehydes, 4-(2-aroylvinyl)thiophene-3-carbaldehydes, or 2-(2-aroylvinyl)nicotinaldehydes have been reported to give furo[3,4-fin[l,2]oxazin-4-ones, thieno[3,4-d][l,2]oxazin-4-ones, or pyrido[3,2-fiG[l,2]oxazin-5-ones, respectively (Scheme 196). " ... 

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