Heterocydes

Hetero)cyclic hydrocarbons Ln.J T.n.J L beginning of a carbocyclic ring T beginning of a heterocydic ring n number of atoms of the ring system f termination of the ring system... 

Heterocyde syntheses are often possible from difunctional open-chain precursors, including olefins as 1,2-difunctional reagents, and an appropiate nucleophile or electrophile containing one or more hetero atoms. The choice of the open-chain precursor is usually dictated by the longest carbon chain within the heterocyde to be synthesized. 

Many successful regioselective syntheses of heterocydes, however, are more complex than the examples given so far. They employ condensation of two different carbonyl or halide compounds with one nitrogen base or the condensation of an amino ketone with a second difunctional compound. Such reactions cannot be rationalized in a simple way, and the literature must be consulted. 

In addition to benzene and naphthalene derivatives, heteroaromatic compounds such as ferrocene[232, furan, thiophene, selenophene[233,234], and cyclobutadiene iron carbonyl complexpSS] react with alkenes to give vinyl heterocydes. The ease of the reaction of styrene with sub.stituted benzenes to give stilbene derivatives 260 increases in the order benzene < naphthalene < ferrocene < furan. The effect of substituents in this reaction is similar to that in the electrophilic aromatic substitution reactions[236]. 

Besides the classical heterocydization and ammonolysis methods some other syntheses have been developed to prepare secondary and tertiary... 

In this section, only salient features of the synthesis, physicochemical properties, and reactivity of major derivatives of 2-aminothiazole and 2-imino-4-thiazoline are summarized. Further details on each compound are found in associated references collected in Section VII. The synthetic methods reported in this section exclude heterocydization methods treated in Chapter II but given in specific references found in Section VII. 

These compounds are easily prepared from the appropriate 2-aminothiazole and acyl chloride (see Section III.2.D) or by general heterocydization methods. Acyl chlorides may be replaced by the corresponding anhydrides (471). Acids themselves may be used as acylating agents provided that the imidazole-triphenyl phosphine mixture is used as a catalyst (472). The Curtius degradation of 247 yields 2-acetamido-4-phenylthiazole (248) (Scheme 149) (473). 

The symbol stands here for a succession of elementary steps (heterocydization. first deshydratation, second deshydratation). 

A-2-Thiazoline-4-ones are usually obtained by the heterocydization method (38b-388). 2 Alkylthio-4(5)-thiazolones (162) are obtained by alkylation at sulfur of rhodanine (160) in nonpolar solvent (Scheme 85). 

Thiazoles Substituted by Heterocydic Groups Nonadjacent to flie Tbiazole Ring... 

Syntheses of the Pyrimidine Ring from Other Heterocydes... 

Table 34 Operating Conditions for GLC Separation of Five-membered Heterocydes with More Than One Heteroatom ...

Other examples of addition reactions that form carbon-nitrogen bonds are the reactions of hexafluoro-2-butyne with various heterocydes [77], aromatic... 

Figure 4.14 Schemauc represemaiion of (a) 4-membered, (b) 6-membered and (c) 8-membered (LiN) heterocydes showing pendant groups on N lying both above and below the plane of the ring, (d) the laddered structure formed by lateral bonding of iwo l.iiN uniK.

W. Kuriyama and T. Kitahaia, Heterocydes 55,1 (2001). Regaiding the ayntheaia of 1 -methoxytryptophan derivativea, aee an enatum of theae authora. 

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