PART 3 SIX-MEMBERED HETEROCYCLES

Pyridine is a polar, stable, relatively unreactive liquid (bp 115°C) with a characteristic strong penetrating odor that is unpleasant to most people. It is miscible with both water and organic solvents. Pyridine was first isolated, like pyrrole, from bone pyrolysates. Its name is derived from the Greek for fire (pyr) and the suffix idine used to designate aromatic bases. Pyridine is used as a solvent, in addition to many other uses including products such as pharmaceuticals, vitamins, food flavorings, paints, dyes, rubber products, adhesives, insecticides, and herbicides. Pyridine can also be formed from the breakdown of many natural materials in the environment. 

The consequences of this replacement gives pyridine a reduced susceptibility to electrophilic substitution compared to benzene, while being more susceptible to 

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Ketenes as Privileged Synthons in the Synthesis of Heterocyclic Compounds Part 3 Six-Membered Heterocycles... 

Part 2 (Volumes 2 and 3) deals with mono- and poly-cyclic compounds with one or more six-membered heterocyclic ring, with nitrogen, oxygen and sulfur as the heteroatoms. Volume 2 contains the six-membered rings with one nitrogen atom (Part 2A) and Volume... 

Six-membered heterocycles are part of many biologically interesting compounds (Fig. 3.13). 

Ru(CO)3(GeMe)3]3 0.072 Triangle of Ru atoms form part of first established six-membered heterocyclic metal ring system. i... 

Part 2 (2015AHC(114)147). In this chapter, (Part 3), the appHcations of ketenes as a privileged synthon in the synthesis of various six-membered heterocycles, including spiro- and fused ring examples are given. 

Finally, Part 3 in the series Ketenes as Privileged Synthons in the Synthesis of HeterocycHc Compounds by Majid Heravi and Bahareh Talaei at Alzahra University, Iran, describes the use of ketenes as starting materials for the preparation of a wide variety of six-membered heterocycles. 

The continuing interest in the chemistry of the 1,3-oxazines and the related thiazines and pyrimidines may arise in part from their versatile synthetic applicability and their pharmacological usefulness. Although six-membered saturated or partially saturated 1,3-heterocycles and their derivatives fused with a benzene ring have been thoroughly studied since the beginning of the twentieth century, much less attention has been paid to their saturated counterparts, the related cycloalkane-fused bicyclic 1,3-heterocycles. 

The zwitterion 32, Equation (3), has an unusual structure in the solid state in which a cationic tetrahedral Al(lll) center and a planar carbanion are both part of a six-membered ring <19980M3135>. NMR spectroscopy suggests that this unusual structure is retained in solution. The X-ray crystal structure of 33 (M = Si) shows the heterocycle to be almost planar with the tin atoms being inequivalent. This inequivalence is also seen in the solid-state Sn NMR spectrum <20000M3272>. 

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