Annelation review

C,0-ambident -, acylation 10, 622 O-acylation 10, 622s31 Anion specificity 31, 452 Annelation -, review 31,948... 

This chapter describes the chemistry of the simple, nonfused 1,2,4-triazoles including those triazoles annelated by a saturated ring. A resume of the most important points discussed by Polya in the corresponding chapter in the first edition of Comprehensive Heterocyclic Chemistry (CHEC-I) <84CHEC-1(5)733> has been made and a substantial number of the earlier references have been retained, but this account will concentrate on those advances that have been made in this area since the early 1980s. A comprehensive review of 1,2,4-triazole was published in 1981 <8lHC(37)l>. 

A number of monocyclic and benzo-annelated examples of 1,2- and 1,3-thiazepines have been prepared but there has been little systematic study of these systems. The interesting photochemical interconversions of pyridine N-imides into 1,2- and 1,3-diazepines and of pyridine Af-oxides into 1,2- and 1,3-oxazepines regrettably lack parallels in thiazepine chemistry. There has been more interest in 1,4-thiazepines, as both rearrangement products and possible biogenetic precursors for penicillins and because of the pharmacological value of the benzo- and dibenzo-[l,4]thiazepines as antidepressants and coronary vasodilators. The only review (70ZC361) is excellent but not very recent. 

The subject of this review is a systematization of synthetic methods for constructing a skeleton of a peri-heterocyclic nucleus (with closed-loop and nonclosed-loop 7r-systems) from precusors that do not contain such a nucleus. Conversions of peri-annelated heterocyclic rings and recycli-... 

Volume 51 of Advances consists of three chapters, V. V. Mezheritskii and V. V. Tkachenko (Rostov-on-Don, U.S.S.R.) review the synthesis of peri-annelated heterocycles, a large and interesting class which has not previously been treated in a systematic fashion. R. M. Acheson (Oxford, U.K.) provides the first detailed survey of 1-hydroxypyrroles and their benzo derivatives, compounds which show an interesting and unusual chemistry. Finally, B. A. Trofimov (Irkutsk, U.S.S.R.) describes the minifold preparative possibility for pyrroles from ketoximes and acetylenes, a reaction discovered by Trofimov and developed by him into a most important entry into pyrrole chemistry. 

The goal of the present review is to demonstrate the wide potential for using newly developed methods to synthesize 2-benzopyrylium salts and to discuss in detail the numerous and unusual transformations of this class of oxygen cations in comparison with monocyclic pyrylium salts, i.e., the study of influence of benzo[c]annelation. 

The first available review of annelated 1,5-benzothiazepines, a diverse group of increasingly important polycycles, is provided by A. Chimirri and her colleagues (Messina, Italy) in Chapter 2. Recent developments in the chemistry of pyrido[l,2- ]pyrimidines are covered in Chapter 3 by... 

When recent advances in the chemistry of isoxazoles were reviewed by Kochetkov and Sokolov1 in this Series in 1963 (and by Quilico2 in 1962), the main features of isoxazole chemistry had been established. Since then some important new discoveries have been made, but probably the most significant advances have concerned the exploitation of the known features of their chemistry in synthesis. Particularly noteworthy developments include the further application of the cycloaddition of nitrile oxides in the synthesis of isoxazoles (Section II,C and D), the use of isoxazolium salts in peptide synthesis (Section III,B,2), syntheses involving the products of reductive cleavage of isoxazoles as intermediates (Section III,D and E) and annelation reactions via deprotonation of alkylisoxazoles (Section 1II,E). 

Review. Vollhardt has reviewed the use of cobalt-catalyzcd [2 + 2 2] cycloadditions for synthesis of annelated benzenes, pyridines, and other heterocycles, as well as of complex natural products,... 

Although it is not within the scope of the review, the effect of annelation to give three-membered heterocycles, e.g. aziridines, oxiranes, thiiranes and thiirane S-oxides, was also investigated. One particularly striking result might be mentioned this concerns the C-NMR spectrum of 55 with respect to 54. The chemical shifts of C(3) in 55 and 54 are 31.4 and 8.4 ppm respectively, and the derived S shift is without precedent on the other hand... 

Structural aspects of heterocyclic systems that contain a metal heteroatom have been little explored. Such a wealth of data is available for carbocycles that these will be used as initial structural models for the organometallic systems. The questions related to the effect of replacing a —CHg— group in a carbocycle by a metal atom are many-sided. In the next few paragraphs the structures of carbocycles and their benzene-annelated derivatives will be briefly reviewed, followed by a discussion of the problems introduced, or changes that may be expected, upon heteroatom replacement. Then the data observed for organometallic systems will be discussed in terms of the points raised in these sections. 

The annelation reactions which have found numerous applications in steroid synthesis, including the construction of fifth rings, have been reviewed. ... 

This review covers nonannelated and annelated eight-membered heterocycles containing one nitrogen. However, it does not include polycyclic structures where nitrogen is the bridgehead atom (1), nor where nonadjacent ring carbons are linked by a bridge (2). 

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