Elimination nitrogen, ring contraction

The reaction of cyanogen azide with enamines of cyclic ketones to yield a cyanoamidine with one less member in the carbocyclic ring represents a potentially valuable method of ring contraction under mild conditions (199a). The reaction probably proceeds first by 1,3 cycloaddition of the azide to the enamine followed by rearrangement and elimination of a molecule of nitrogen. 

The photolysis of cyclic diazo ketones in hydroxylic solvents leads to ring contracted carboxylic acid derivatives via this ketocarbene -> ketene rearrangement. Examples of such reactions are given in (2.24)239) and (2.25) 240). In this last example a photoequilibrium between the diazo ketone and its valence isomer, a diazirine, has been observed, both products then eliminating nitrogen to afford the cyclobutane carboxylic acid. 

The synthesis of li7-cyclopropa[/]phenanthrene (142) presented unexpected difficulties and met many failures. Early approaches used a variety of schemes which were not adequate for this highly reactive compound and invariably produced ring-opened products. Thus irradiation of the substituted indazole 138 resulted in nitrogen extrusion and formation of the biradical 139, which reacted with the solvent, benzene, to form 140. The desired cycloproparene 141 was not formed. Ring contraction of 144, in turn, produced derivatives of 9-phenanthroic acid, the formation of which was shown not to involve phenanthrocyclopropenone (143). °° The attempted 1/3/elimination of 145 was similarly unsuccessful and afforded no 142. ... 

Derivatives of triazole have been obtained by Fusco et al,280 from phenyl azide and 1-morpholinocyclohexene. Their decomposition leads to cyclopentanecarboxylic acid by elimination of nitrogen and ring contraction.281 The dienamine obtained from piperidine and... 

A carbon-nitrogen bond is broken during a chemical follow-up reaction in many ring closures or ring contractions [192] of heterocyclic compounds in which a nucleophilic attack on an imine followed by an elimination of the amine or ammonia takes place. This is discussed in Chapter 18, in which is also mentioned the loss of ammonia from the primarily formed dihydro compound in the reduction of certain aminoheterocyclic compounds. 

The reaction between a diazocarbonyl compound and an electron-deficient alkene is carried out in the presence of an additive that suppresses the 4,5-dihydro-3 f-pyrazole to 4,5-dihydro-l/f-pyrazole isomerization, thus allowing the ring contraction of the 4,5-dihydro-3//-pyrazole by thermal nitrogen elimination to occur under the reaction conditions. 

Quinonediazides, which are of commercial value as photoresists, undergo analogous ring contraction on photochemically induced elimination of nitrogen. 

The irradiation of the acetate (183) in t-butyl alcohol under nitrogen gave the product (184).187 The ring-contraction in this example can be interpreted in terms of Norrish Type I fission followed by elimination of isobutene and... 

On irradiation, 2,6-bis(diazo)cyclohexanone (104) also undergoes elimination of nitrogen accompanied by ring contraction.84 A cyclopropenone (105) rather... 

The first step in the reaction scheme involves the elimination of nitrogen from the diazoquinone (VI), forming a carbene (VII). The carbene undergoes a Wolf rearrangement, involving ring contraction, and leading to the formation of ketene (VIII). In the presence of small amounts of water in the novoiac binder," hydration of the ketene leads to the formation of indene carboxylic acid (IX). The main feature of the process is the transformation of a fairly hydrophobic... 

The general synthetic methods for [2.2] CPs have been already estabhshed. Most of them employ the ring contraction reactions of the 2,11-diheteroatom-substituted [3.3]CPs. Photochemical ehmination of sulfur or selenium atoms from [3.3] CP-2,11-disulfide or diselenide and flash vacuum pyrolysis of sulfur dioxide obtained by the oxidation of the corresponding sulfides are the most general methods. 2,11-Diaza[3.3]CPs are converted to the corresponding [2.2]CPs via their nitroso derivatives by reductive elimination of nitrogen. " Photoextrusion reactions of COj from cychc diesters can also be appHed to the synthesis of [2.2]paracyclophanes (PCPs)"- and [2.2]heterophanes, as described below. "... 

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