Six-membered heterocycles with two heteroatom

Six-membered heterocycles with two heteroatoms are prepared by reaction of diketene with a substrate containing a C—O or C—N multiple bond. With carbonyl compounds diketene reacts in the presence of acids to give l,3-dioxin-4-ones. The best known is 2,2,6-trimethyl-4H-l,3-dioxin-4-one [5394-63-8] (15), the so-called diketene—acetone adduct, often used as a diketene replacement that is safer to handle and to transport, albeit somewhat less reactive than diketene itself (103,104), forming acetylketene upon heating. 

Fig. 3.10 Six-membered heterocycles with two heteroatoms obtained by solid-phase chemistry. Seven-membered heterocycles...

DIMEDONE-ANNULATED SIX-MEMBERED HETEROCYCLES WITH TWO HETEROATOMS... 

Synthesis of Six-Membered Heterocycles with Two Heteroatoms 4.2.2.1 Pyrimidines and Pyrimidinones... 

A few more examples of microwave-induced synthesis of medicinally important six-membered heterocycles with two heteroatoms are provided in Table 4 and Figure 15). 

Application of Ionic Liquids in Heterocyclic Synthesis 4 1 Synthesis of Five-Membered Heterocycles 4.1.1 Synthesis of Five-Membered Heterocycles 443 443 with Two Heteroatoms 4.2.3 Synthesis of Six-Membered Heterocycles with Three Heteroatoms 4.3 Synthesis of Some Other Spiro Heterocycles 468 479 480... 

The tricyclic compounds 35 are among the most studied six-member Te-containing heterocycles with two heteroatoms in the ring. The first representive... 

There are two important general types of reaction by which six-membered heterocycles containing two or more heteroatoms can be transformed into other six-membered heterocyclic systems, namely reactions which involve an ANRORC mechanism, and reactions which proceed by a Diels-Alder/retro-Diels-Alder type of mechanism. Transformation of 1,3-oxazinones and -thiazinones into pyrimidones (equations 193 and 194) has been extensively used, especially in the conversion of isatoic anhydride into quinazolinones (e.g. equation 195). 2,4-Diaryl-l,2,3,5-oxathiadiazines, which are readily accessible by reaction of sulfur trioxide with aryl isocyanates, are useful precursors to pyrimidines and 1,3,5-triazines (equation 196). 

Sainsbury M (1996) Six-membered rings with two or more heteroatoms with at least one selenium or tellurium. In Katritzky AR, Rees CW, Scriven EFV (eds) Comprehensive heterocyclic chemistry II. Pergamon, Oxford, chap 6.24, p 878... 

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