Nitrogen ylide cyclizations synthesis

Another interesting use of nitrogen ylides in synthesis was reported by Williams and Miller who employed this intermediate in the preparation of a bicyclo P-lactam. P-Lactam 152 was formed in a single step from the diazo precursor 150.68 The proposed mechanism involves a Rh(II)-catalyzed generation of ammonium ylide 151 which abstracts a proton from the benzylic position and then undergoes N-0 bond heterolysis to generate the cyclized product and benzaldehyde. 

APPLICATION OF NITROGEN YLIDE CYCLIZATIONS FOR ORGANIC SYNTHESIS... 

Beall, L. S., Padwa, A. Application of nitrogen ylide cyclizations for organic synthesis. Advances in Nitrogen Heterocycles 1998, 3, 117-158. 

Intramolecular acid- or rhodium [II]-cataIysed carbene nitrogen-hydrogen insertion from iodonium ylide intermediates was used in an efficient synthesis of 1-/1-methylcarbapenems the cyclization products had different stereoselectivity, depending on the catalyst [11] ... 

Carbene reactions provide a versatile approach to the synthesis of five-membered nitrogen-containing rings. Of particular importance here are intramolecular insertion of a carbene into C — H and N — H bonds, addition onto multiple carbon-carbon bonds, intermediate formation of ylides as a result of carbene addition onto the heteroatom followed by rearrangement, cycloaddition, and cyclization. 

Nitrogen Systems.—Monoaza-compounds. Treatment of the azapentalene anion (745) with dichloromethane and butyl-lithium yields a mixture of indolizine (746 R = H) and compound (747) it has been established that the latter is not a precursor of indolizine.3-Diethylaminoindolizine (746 R = NEt2) is formed by the reaction of 2-bromopyridine with propargyl alcohol and diethylamine in the presence of bis(triphenylphosphine)palladium(ll) dichloride and copper(i) iodide. The pyridinium ylide (748) undergoes 1,5-dipolar cyclization to the tran -dihydroindolizine (749). As in previous years, there have been several reports on the synthesis of the indolizine ring system from pyridinium ylides the methide (750 R = H, R = Ph) adds benzylideneacetophenone to form the tetrahydroindolizine (751), the action of phenyl vinyl sulphoxide. 

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