Nitrogen-containing heterocycle synthesis seven-membered ring heterocycles

Under strictly anhydrous conditions, the iminophosphorane intermediate that is formed as a result of the Staudinger reaction can react with aldehydes and ketones in an intermolecular fashion (as in the synthesis of imine 36 described above) or intramolecularly with a variety of carbonyl containing functional groups to afford a host of products. Nitrogen containing ring systems such as cyclic imines (44) represent just one of the many products one can prepare and the reaction is particularly well suited for the facile synthesis of five, six, and seven-membered rings. In addition to aldehydes and ketones, carboxylic acids, esters, thio-esters, and amides can also react in an intramolecular fashion to trap an iminophosphorane to afford a variety of heterocycles. Examples from the current literature are described in Section 2.5.5. 

There are several reviews, which are devoted to the synthesis of seven-membered heterocycles, but rings with four or more heteroatoms are not typically described in these reviews <888569,9isi8i>. Only a few of the possible heterocyclic structures are actually known most contain nitrogen and... 

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