Nitrogen Insertion Reactions of Ring Compounds

The most important nitrogen insertion reactions are still the Schmidt and the Beckmann rearrangements and their modifications. Yet, a number of other nitrogen insertion reactions are known, and examples will be therefore given and discussed. 

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The photoelimination of nitrogen from diazo compounds provides a simple and versatile route for the generation of carbenes, and in certain instances, insertion reactions of carbenes can be employed in the synthesis of heterocycles. Carbenes are believed to be involved at least in part in the photochemically induced conversion of N,N-diethyldiazoacetamide (439) into the y-lactam 440 and the /Mactam 441,365 and a similar approach has been successfully employed in the synthesis of a carbapen-2-em366 and of 7-methylcephalosporin analogues.367 Carbene insertion of a different type has been observed on irradiation of the 6-anilino-5-diazouracils 442 to give the indolo[2,3-d]pyrimidines 443.368 Ring contractions in heterocycles... 

The electron-rich and cyclically conjugated 8 rr electron system of 1,4-dihydropyrazine can be stabilized in essentially planar conformation by organosilicon substitution at the enamine nitrogen centers [1], In addition to electron transfer [1] and triorganosilyl exchange reactions [2], we have explored the possibility of inserting heterocumulenes X=C = Y into one or both of the N-Si bonds of the compounds 1 in order to functionalize this unusual ring structure [3],... 

The properties of 5-azido and 5-diazomethyl-l,4-diphenyltriazole are unusual in that both compounds lose nitrogen under very mild conditions. The products derived from the azide are mainly those of ring cleavage (Section IV, G), but the diazoalkane gives a carbene which undergoes addition and insertion reactions with several solvents. These reactions are illustrated in Scheme 49. 

One of the key steps in building the fused ring involves the reaction of the activated acetoacetate methylene group in that compound with toluenesulfonyl azide to give the diazo intemediate (12-1). Treatment of that product with rhodium acetate leads to a loss of nitrogen with the consequent formation of carbene (12-2) this inserts into the adjacent amide N—H bond to form a five-membered ring and thus the carbapenem (12-3) [15]. The first step in the incorporation of the thioenol function consists in the conversion of the ketone to the enol phosphate derivative... 

The reaction of a nitrogen-substituted silylene (88) with a 2H-azaphosphirene (87) gave a bicyclic compound (89), which contains an Si-Si bond and a tungsten-bound carbene.96 Compound (89) was isolated in 62% yield and its crystal structure was described. However, when an extra phosphorus atom was inserted into the ring as in (90), the monocyclic (91) was isolated in 90% yield. A crystal structure for (91) was also reported. 

Carbonylation with aUcenylation is one of the most important reactions in the application of intramolecular five-membered ring compounds. Heterocyclic ketones are synthesized by the insertion of carbon monoxide into a metal-carbon bond followed by demetalation reactions. Because metal-carbon or metal-nitrogen a-bonds are... 

Again, the main reactions correspond to formal insertion of the ring-opened cyclopropen-one (or -thione) into the C—N bond rather than into the C—C bond of the unsaturated nitrogen compounds. The comparable reactions of (431) with l-azirines and of enamines and ynamines with substituted methylenecyclopropenes have recently been reported. 

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