Seven-membered nitrogen heterocycles

This methodology has been applied to the diastereoselective synthesis of the pyrrolizidine alkaloid 196 from 194 via 195 (Scheme 15.62) [123], Furthermore, the diastereoselectivity of these reactions for different dipolarophiles has been investigated in detail [124] and could be extended to a ring closure to seven-membered nitrogen heterocycles [125,126]. 

In this section I refer to a number of cycloadditions which cannot be categorized into the above-described types. For example, Murai and colleagues reported the four-component coupling of alkyne, hydrazone, hydrosilane and CO. Here, the [Ir4(CO)i2]-catalyzed reaction proceeded under pressurized CO conditions at high temperature, whereby a seven-membered nitrogen heterocycle was obtained (Scheme 11.37) [48]. 

The generation and reactivity of conjugated azomethine ylides has been reviewed.148 1,3-Dipolar cycloaddition and 1,5- and 1,7-electrocyclizations have been described as powerful strategies for the synthesis of monocyclic and annulated five- and seven-membered nitrogen heterocyclic compounds. 

Although the chemistry of the benzazepines has received considerable attention over the past seven decades, only brief reviews have so far appeared Moore and Mitchell2 treated the chemistry of the benzazepines in the context of other seven-membered nitrogen heterocyclics and the synthesis of 3-benzazepines has been briefly reviewed by Gardent.3... 

Diels-Alder reaction of the allenic dienamides (111). The corresponding cis-indolidines and indoles are readily prepared from the products (112) by standard reductive and oxidative methods, respectively. The fused five-, six-, and seven-membered nitrogen heterocycles (114) can be prepared in excellent yields from the... 

Fort used carbene ligands for intramolecular aminations, yielding five-, six- and seven-membered nitrogen heterocycles [97]. 

Rapoport and co-workers have reported a general synthesis of nitrogen, oxygen, and sulphur heterocycles (218) by rhodium-catalysed intramolecular N-H, 0-H, or S-H insertion reactions.of keto-ester precursors (217)- This reaction is well documented as an efficient route to B-lactams but this group has now shown that the reaction works well for the synthesis of five-and six-membered nitrogen heterocycles (Scheme 22). The reaction fails for seven-membered nitrogen heterocycles in this case C-H insertion to give a eyelopentanone is the preferred reaction mode. 

Six- and seven-membered nitrogen heterocycles may be made by a newly reported reaction of the mesoionic oxazolone (438) with cyclopropenes and cyclobutenes, respectively (Scheme 61). Similarly, compound (438) reacts... 

---