Double bonds nitrile imine -cycloaddition reactions

I.3.4.2. Intermolecular Cycloaddition at C=X or X=Y Bonds Cycloaddition reactions of nitrile oxides to double bonds containing heteroatoms are well documented. In particular, there are several reviews concerning problems both of general (289) and individual aspects. They cover reactions of nitrile oxides with cumulene structures (290), stereo- and regiocontrol of 1,3-dipolar cycloadditions of imines and nitrile oxides by metal ions (291), cycloaddition reactions of o-benzoquinones (292, 293) and aromatic seleno aldehydes as dipolarophiles in reactions with nitrile oxides (294). 

Some features are characteristic of reactions of nitrile oxides with 2,4,6-cyclo-hep tatrien-l-imines (8-azaheptafulvenes). 1,3-Dipolar cycloaddition to the C=N double bond of N-aryl-2,4,6-cycloheptatrien-l-imines 142 (R = Ar), affording... 

Variously substituted nitrile imines are easily available and react readily with a wide range of double and triple bonds. Intermolecular cycloaddition is therefore an area of major interest, and a large proportion of the papers on the use of nitrile ylides in synthesis is concerned with the exploitation of this reaction. Space limitation means, regrettably, that work leading to results that were predictable on the basis of known chemistry (19) has generally not been included. 

Trifluoroacetylacetonitrile (396) can also react with nitrile imines 395 via two reaction paths depending on their structure. Those with an electron donating N substituent reacted via cycloaddition to the enolic double bond to give 397 while... 

Numerous [3 + 2] cycloaddition reactions have been performed with bis(trifluoromethyl)-substituted azomethine imines (79CB2609,79LAI33). Noteworthy is the [3 + 2] cycloaddition reaction with tetracyanoethylene, which adds across one of the nitrile functions instead of adding across the CC double bond. This is one of the rare examples of this type of periselectivity found in the case of tetracyanoethylene in [3 + 2] cycloaddition processes (76LA30). 

The double bonds of the thiophene skeleton can be exploited as a 2-component in 1,3-dipolar cycloaddition reactions. The first examples of an intramolecular addition of nitrile imines 73 to give products 74 and 75 are shown in Scheme 7 <1998J(P1)4103>. 

The triazolines resulting from the various reaction schemes are predominantly A2-compounds the cycloaddition reactions of azomethinimines and nitrile ylides lead to A3-triazolines. The amidrazones are unique a A3- or A2-system results, depending on the presence or absence of N-2 substitution (84KGS1415). The rare A -compounds are presumed to result from the nonregioselective addition of diazomethane to the imine double bond (72LA9) or by fluorination of 3,6-diamino-s-tetrazine (67USP3326889 70USP3515603). 

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