Michael iminophosphoranes

Additionally, uracil 6-iminophosphorane, isocyanate, and o-methyl-e-caprolactim ether join to form the intensely yellow pyrimido[4 5 4,5] pyrimido[6,l-n]azepine (360), as shown in Scheme 130. Upon ring closure, methanol is spontaneously eliminated. Diethyl azodicarboxylate affords with the other components pyrimido[4,5-e][l,2,4]triazoline (361), which is closely related to the alkaloid isofervenuline. The imidazo[5, -/][ ,2,4]tria-zine (362) results in a known Michael-type rearrangement sequence by treatment with diethyl acetylenedicarboxylate (86JOC149, 86JOC2787) in this latter case, the Michael-type addition occurs much faster than the expected three-component reaction [93H(35)1055]. 

In a more recent approach, 6-aminouracil or its 6-iminophosphorane is reacted with A -phenylbenzimidoyl chloride to give, in a Michael-type addition, a tautomeric pair of imines, A and B. The equilibrium is shifted in different solvents. Tautomer B is intercepted by an acetylenic ester to form a l,4-dihydropyrido[2,3-c/]-pyrimidine. The iminophosphorane of A and isocyanate results in an aza-Wittig reaction and polar 67r-electron cyclization reaction to give pyrimido[4,5-[Pg.159]

The commercially available polystyrene-supported iminophosphorane (PS-BEMP) 55 (Figure 3.1) has been utilized to promote the Michael addition of acyclic- and cyclic-1,3-dicarbonyl compounds, including those substituted at the active methylene, to electron-poor olefins. 

DihydroquinazoHnes have been synthesized by aza-Wittig coupling to form the carbodiimide and subsequent addition of a secondary amine to induce an intramolecular Michael addition of 157 [202], Elements of diversity are therefore added upon treating the iminophosphoranes with isocyanates or thioisocyanates, and upon the subsequent reaction of the carbodiimide with an excess of a secondary amine. 1,4-DihydroquinazoHnes have been prepared using a tetrafunctional scaffold cyclized with aryl isothiocyanates on Rink resin [204],... 

Michael addition reaction of various p-ketoesters with several Michael acceptors in water containing 10mol% of A7-phenyl-tris(dimethylamino)iminophosphorane results in high yield conversion to the corresponding adducts [26] (Scheme 5.11). 

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