3/6-annulated systems

Thionin 1 (X = S) is unknown only annulated systems have been reported which exhibit no aromatic character. 

The bicyclic system 5 can also be used to prepare annulated systems by cycloaddition-cycloreversion processes. With 2//-pyran-2-one (6) a mixture of cycloadducts is formed on... 

In an analogous reaction, treatment of 9 (R = Ac, C02Me) with 2,6-diphenyl-l,2,4,5-tetrazine leads to the annulated system 10.15... 

An unusual combination, namely a Michael addition and a Simmons-Smith reaction, has been elaborated by the group of Alexakis [112]. Using their protocol, 3/5-as well as 3/6-annulated systems can easily be obtained, which might be useful as precursors for the total syntheses of (-)-(S,S)-clavukerin A and (+)-(R,S)-iso-clavukerin, both isolated from Clavularia koellikeri [113]. 

The present review covers the Thorpe-Ziegler syntheses of 3-aminofurans, 3-aminopyrroles, 3-aminothiophenes, 3-aminoselenophenes, and diverse aminoazoles as well as the corresponding annulated systems that appeared from 1983 to 1996 but excludes examples considered in the 3-cyanopyridine review (92MI1). Moreover, examples are included that do not report a separate Thorpe-Ziegler cyclization but are likely to involve this type of reaction (e.g., cases in which precursors 1 were not isolated and identified but directly formed in the reaction mixture). Special attention is paid to synthetic aspects, although some reaction mechanisms are discussed too. 

Formation of dicationic salts based on 1,5-dithia- and 1,5-diselenacyclooc-tanes and the respective benzo- and naphtho-annulated systems 93PS(74)261. 

Even cyclophanes containing large aromatic units such as pyrene, anthracene, or benzophenanthrene units or partially hydrogenated annulated systems can easily be desulfurized via sulfone pyrolysis, as Staab et al. have shown in a series of works on such compounds [49 53],... 

Not only annulated systems but also oligophenyls were successfully prepared by sulfone pyrolysis (cf. 127, 129, and 131) [54, 55],... 

Bridged systems [i,/ -annulated systems withy -1 = 2-4. Types V-IX... 

Only ortho-condensed systems [iV.vl ,/ m,n]-annulated systems with j-i=loT5,l-k = n-m=l. Types XVI-XVII... 

With a discussion of the 6e electrocyclic reactions of acyclic (Section 6.2.2.1) and mono-annulated hexa-l,3,S-trienes (Section 6.2.2.2.1) completed, it may be apparent to the reader that the topic of bis-an-nulated systems (this section) and higher-order annulated systems (Section 6.2.2.2.3) may be considered fairly direct extensions of the lower-order annulated systems. Accordingly, only a selection of the major types of bis- and higher-order annulated systems (presented in the order, types XI, XV and XIII and then Mgher-order annulated systems) will be presented. 

First representatives of the previously unknown tricyclic annulated system, viz., ethyl 7-methylthio-4,5-dihydro-3//-thieno[2,3,4-step synthesis from 4,6-dichloro-2-me-thylthiopyrimidine-5-carbonitrile (2000MI3). 

This type of double dehydrobromination has also been used in a few syntheses of 1,6-methano-annulated systems in which the initially formed norcaradiene isomerizes to the corresponding cycloheptatriene derivative. Thus, a good yield of bicyclo[4.4.1]undeca-l,3,5,7,9-pentaene (11, X = H) was obtained by treating the corresponding tetrabromide (9, X = H) with methanolic potassium hydroxide. The 11,11-difluoro analog 11 (X = F) was likewise obtained in 80% yield. The 11,11-dichloro (X = Cl) and 11,11-dibromo (X = Br) analogs, however, were ob-... 

The cis or trans configuration of the annulated system normally is not changed in nucleophilic substitution. Such a cisitrans isomerization, however, has been observed in a few nucleophilic substitution reactions of various bicyclo[9.1.0]dodecane derivatives. ... 

The known examples of the synthesis of higher-order annulated systems (exemplified by types XVI-XVn in Figure 2) involve photochemical cyclization followed by oxidation arene analogs of stilbenes. 

The atom transfer methodology is used in the formal total synthesis of racemic albene82. Addition of 1-butynyl radicals to an activated norbornene derivative occurs exclusively from the. w-face. and consecutive cyclization yields the rw-cvu-annulated system. Conversion of the anhydride to the dimethyl ether and reductive deiodination yields the intermediate diester. Further transformations give 3, a direct precursor to albene, in 32% overall yield. 

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