Reaction with ketenimines

In the [3+2] cycloaddition reaction with ketenimines two isomeric adducts 12 and 13 are formed by reaction across either the C=C or the C=N bond of the ketenimines . 

Trimethylsilyldiazomethane reacts with n-butyl lithium to give Me3SiC(Li)N2, which undergoes a [3+2] cycloaddition reaction with ketenimines to give the 1,2,3-triazoles 93 in 67-82 % yields... 

Azacycloheptatrienylidene (4b), the aza analogue of cycloheptatrienylidene (4a), has on occasion been postulated to be the product of the ring expansion of lb.la In contrast to the case with 34a,lla 34b has never been directly detected. However, Iwamura and co-workers have reported chemical trapping of 4b and its o-phenyl derivative (4c) by tetracyanoethylene (TCNE), as shown in Scheme 15 49 While the product in Scheme 15 is formally the product of reaction of 4b with TCNE, the authors noted that it could also arise from reaction of TCNE with ketenimine 3b. 

Having explored the scope of this reaction, it was then possible to use an optically active phosphoramidate (232.d), derived from (5)-a-methyl-benzylamine, to perform a kinetic resolution procedure.134,138 Upon reaction of 221 with 0.5 equiv of the phosphoramidate anion 232.d, selective reaction with the 7 -isomer of 221 resulted in an enhancement in the proportion of 5-221 along with the expected ketenimine products (233). The absolute configuration of i -233.d was determined by X-ray crystallography, and thus all other absolute configurations assigned by comparison of CD and HPLC data.39,138... 

Experimental observations support these views. Photolysis of 1-naphthylazide in the presence of diethylamine and tetramethylethylenediamine (TMEDA) yields azirine, but no ketenimine-derived adducts at ambient temperature. " In the presence of diethylamine but in the absence of TMEDA, good yields of 1-amino-naphthalene and 1,1 -azo-naphthalene, products attributable to the triplet nitrene are observed. Good yields of 46 are also achieved when the photolysis of 1-naphthylazide and diethylamine is performed at —60 °C in the absence of TMEDA. Presumably, lowering the temperature extends the hfetime of azirine 43 by reducing its rate of reversion to singlet 1-naphthylnitrene more than it retards the rate of its reaction with diethylamine. 

Several ketenes have been converted into l,2-dioxetan-3-ones by reaction with triphenyl phosphite ozonide (77JA5836), and ketenimines form cyclic iminoperoxides with photochemi-cally generated singlet oxygen (Scheme 97) <79AG(E)788,80CC898). 

Annelatlon reactions. The ketenimine 1 acts chemically as a vinyl phosphonate activated by the cumulated imino group and is useful as an annelation reagent for the synthesis of heterocyclic compounds. As such it condenses with the sodium salt of salicylaldehyde (2) to afford the benzopyrane in 3 in 52% yield. Similarly, the pyrrolizine 5 is available from the sodium salt of 2-formylpyrrole in 51% yield. ... 

There are only few reports of [2 + 2] cycloadditions with ketenimines. " In most cases, reactions occur across the C=C bond. Only ynamines and polyfluorinated alkenes cycloadd to the C=N bond. 

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