Vinyltriphenylphosphonium salt mediated synthesis of 1,4-benzoxazine and coumarin derivatives

Synthesis of Aza Coumarines by Nucleophilic Addition of Acetylenic Esters Catalysed by Ph3P

“…Mechanistically, 15,16 it is conceivable that the reaction involves the initial formation of a zwitterionic intermediate between Ph 3 P and the acetylenic compound and subsequent protonation of reactive 1:1 adduct followed by electrophilic attack of vinyltriphenylphosphonium cation on the aromatic ring at the ortho position relative to the strong activation group. The product is presumably produced by intramolecular lactonization of the unsaturated diester 5 (Scheme 2).…”

“…[10][11][12][13][14] We have recently described a new and operationally convenient approach to the synthesis of carboxymethyl coumarines based on aromatic electrophilic substitution reaction between the conjugate base of substituted phenols, catechol, resorcinol, hydroquinone, and pyrogallol. 15,16 In continuation of our current interest in the development of new routes to heterocyclic and carbocyclic systems, [17][18][19] we report here a simple one-pot synthesis of functionalized 5-Aza coumarines 3, 4. Thus, reaction of 3-hydroxypyridine 1 with dialkyl acetylenedicarboxylate 2 in the presence of triphenylphosphine leads to the corresponding coumarins 3, 4 (Scheme 1).…”

Synthesis and biological evaluation of novel angular fused Pyrrolocoumarins

“…A similar mechanism has been suggested for the formation of coumarins from the reactions between 2, 3 and phenols. [28,29] On the basis of analogous literature data for the reaction of 2-naphthol with phosphites in the presence of DMAD, [30] it is reasonable to assume that the intermediate ylides 12a,b (Scheme 2) are formed by attack of the carbon atom of the anion 4 to the initially formed adducts 11a,b. Hydrolysis of ylides 12a,b followed by lactonization of the resulted intermediate succinate 13 leads to the dihydro-compound 14.…”

Reaction between isocyanides and dialkyl acetylenedicarboxylates in the presence of 4,5-diphenyl-1,3-dihydro-2H-imidazol-2-one. One-pot synthesis of 5H-imidazo[2,1-b][1,3]oxazine derivatives

“…[3][4][5][6][7] Only a few synthetic methods have been reported for the preparation of imidazo[2,1-b] [1,3]oxazine ring systems. [8][9][10][11] As part of our current studies on the development of new routes in heterocyclic synthesis, [12][13][14][15] in this paper we wish to report a facile synthesis of functionalized imidazo[2,1-b]- [1,3]oxazines.…”