Heteroatom-containing systems applications

Scheme 5 Example applications of spin parity to heteroatom-containing systems.

The application of the RCM reaction to the construction of nitrogen-containing ring systems, including quinolizidine derivatives, has been reviewed <1999EJ0959>. From that date, this strategy has become more and more common in quinolizidine synthesis, especially in cases where the cyclization takes place by formation of a bond 7 to the heteroatom. Some examples are given below. 

This regioselectivity was originally one of the greatest unsolved problems in Diels-Alder reaction but with the application of FMO theory, it has now been solved satisfactorily. Calculations made on systems containing heteroatoms give a set of coefficients which account for the observed orientation. 

The structural diversity associated with bicyclic 5-5 fused heterocyclic systems containing two heteroatoms in each ring has been noted previously in both CHEC(1984) <1984CHEC(6)1027> and CHEC-II(1996) <1996CHEC-11(7)115>. In recent years this diversity has also been reflected in the number of applications that have been found for these compounds which include organic metals, molecular clips and receptors and molecular magnets. These fields will be examined in due course through this chapter. 

Abstract This chapter is devoted to recent progress in the chemistry of the 5 5 fused heterocyclic systems. There are four possible modes of 5 5 fusions of the simple five-membered heterocycles leading to four structures containing one heteroatom in each ring. The heteroatoms may be the same or different and may be O, NH, S, Se, Te, P, As, or Sb. The fully conjugated hetero analogs of pentalene dianion have a central C-C bond and are isoelectronic with the 10-7t-electron pentalene dianion. The scope of the chapter is outlined with a survey of various structural types and nomenclature of the parent compounds and their derivatives. New synthetic procedures and synthetic applications of title compounds are presented. This review has concentrated on the new developments achieved from 1997 to September 2007. 

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