Ylides, addition

Dendrimer 27-[GJ can be used as the starting material for the grafting of ylides. Addition of triphenylphosphoranylidene ethenone Ph3P = C=C=0... 

Several reviews on the synthesis of aziridines have been published in the previous year. These publications include a review on the silver catalyzed addition of nitrenes (among other intermediates such as carbene) across a double bond <06EJOC4313> a review on sulfur ylide addition to imines to form aziridines <06SL181> a review on nitrogen addition across double bonds <06ACR194> a general review on functionalization of a,p-unsaturated esters with some discussion of aziridination <06TA1465>... 

Potassium hydroxide when merely dissolved in methanol is not effective in the one-electron reduction of 9-diazofluorene and fluoren-9-ylides. Addition of DMSO to the system makes a drastic change, with the highest efficiency in pure DMSO (Handoo and Kaul 1992, Handoo et al. 1983). 

Few examples of carbonyl ylide additions to Cjq are knovm. A stable tetrahydrofurane adduct 272 (Scheme 4.47) has been prepared based on the generation of the ylide by thermal opening of tetracyanooxiran (TCNE oxide) 270 [316]. 

When acrylonitrile or ethyl acrylate was used as the dipolarophile, the azomethine adducts (134) and (135) were formed no thiocarbonyl ylide addition products were isolable in refluxing toluene or xylene, although the isoindoles (136a) and (136b) derived from them were isolated. In contrast to the reactions with fumaronitrile or AT-phenylmaleimide, the azomethine adducts (134) and (135) were still present at higher reaction temperatures — almost 50% in toluene and 4-5% in xylene. Under the same reaction conditions other electron-deficient dipolarophiles like dimethyl fumarate, norbornene, dimethyl maleate, phenyl isocyanate, phenyl isothiocyanate, benzoyl isothiocyanate, p-tosyl isocyanate and diphenylcyclopropenone failed to undergo cycloaddition to thienopyrrole (13), presumably due to steric interactions (77HC(30)317). 

The benzo derivative (128) reacts as a thiocarbonyl ylide. Addition of N-(p-tolyl)maleimide gives a mixture of the exo (71%) and endo (16%) adducts (129 Ar=p-tolyl), which in hot acetic acid eliminate hydrogen sulfide giving the pyrido[l,2-a]benzimidazole (130 Ar=p-tolyl). Analogous 1 1 cycloadducts (131) are formed with dimethyl maleate, dimethyl fumarate, methyl crotonate and methyl acrylate. In contrast to the transformation (129) —> (130), treatment of the adducts (131 R = H, Me) with hot acetic acid gives the tetracyclic compounds (133) via the benzimidazole derivatives (132 R = H, Me). Reaction with alkynic 1,3-dipolarophiles gives pyrido[l,2-a]benzimidazole (134) by desulfurization of the primary adducts (80CL1369). 

Fig. 14. Regiochemistry of nitrile ylide additions and cycloadditions. (W = electron-withdrawing group)...

The related telluronium ylides also add to a,/3-unsaturated imines through a Michael addition-elimination to the olefin followed by a second equivalent of telluronium ylide addition to the imine, which subsequently eliminates to form aziridines 654 and 655 in a ratio of 13 1 (Scheme 159) <2005JA12222>. 

Alternatively, one can add a carbene source to some form of a C=N bond. This will generate bonds c and b . This model is limited by the availability of cyclic imine or imine-like structures. Several methods are available to prepare aziridines through the functionalization of a C=N bond, although formation of the fused rings will require an intramolecular addition to a pendent imido-bond. The Darzens process and ylide addition to C=N bond are generally not applicable in most cases owing to the structural requirements of the cyclic system. This requirement renders this process less useful overall than the addition to a C=C bond. 

Trost developed a general method of synthesis of vinylcyclqnopanes (and their sulfur and oxygen analogs) through the application of ylide addition to carbmyl compounds. Three major methods involve the cyclopentene annulation, cyclobutanone synthesis, and ring expansion with concomitant alkylation (Scheme 51). °... 

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