Stereochemical Study on 1,3-Dipolar Cycloaddition Reactions of Heteroaromatic N-Ylides with Symmetrically Substituted cis and trans Olefins

Abstract

Stereochemistry of the cycloadditions of twenty-four heteroaromatic N-ylides with several symmetrically substituted cis and trans olefins has been investigated. Cyclic and acyclic cis olefins cycloadd to the and form of the ylides in a highly endo-selective manner giving almost quantitative yields of stereospecific endo 3+2 cycloadducts. N-Ylides stabilized with a substituent of carbonyl type react with trans olefins to form mostly two stereoisomeric 3+2 cycloadducts to the anti form of the ylides. In most cases, they undergo the stereospecific interconversion through a retro cycloaddition process, the isomer ratios and the easiness of transformation depending upon the nature and size of substituents on the five-membered ring which has been built up in the cycloaddition step. On the other hand, N-ylides stabilized with a substituent of noncarbonyl type react with trans olefins to give stereospecific and stereoselective 3+2 cycloadducts as single isomers which are assigned as the cycloadducts to the syn form of the ylides.

1,3-Dipolar cycloaddition reactions of 1-(3-nitrophenacyl)-1,10-phenanthrolinium N-ylide with activated alkynes

“…[1][2][3][4][5] The dipolar 3+2 cycloaddition of dipolarophiles to heteroaromatic N-ylides raises interesting regio-and stereoselectivity problems. [5][6][7][8][9] Recently, the synthesis of a new heterocyclic system, namely pyrrolo[1,2-a] [1,10]phenanthroline, by 1,3-dipolar cycloaddition of 1,10-phenanthrolinium N-ylides with acetylenic dipolarophiles, was described. [9][10][11][12] The extended heteroaromatic system presents helical chirality, like that of the helicene-type compounds.…”

4-(4-Chloro-phenyl)-pyrimidinium ylides. 1. Structure, stability, reactivity

“…According to the literature indications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] the chemistry of cycloiminium ylides is widely discussed. In previous research work we have studied the synthesis, structure, and reactivity of some 1,2-diazinium ylides [12][13][14] (derived from pyridazine and phthalazine) as well as of 1,3-diazinium ylides [15][16][17] (derived from 4-methylpyrimidine).…”

Diazinium carbalkoxy methylides

“…[4][5][6][7] In previous research work we presented a detailed study concerning the syntheses, structure, stability and reactivity of some new 3-p-halophenylpyridazine salts and ylides 8,9 and 4-methylpyrimidine salts and ylides. 10 In these ylides the substituent of the ylide carbanion was a p-R-benzoyl radical with a medium electron-withdrawing effect.…”