Fused compounds

Although the synthesis of thiazolidine-2,4-dithione has been reported (357), no examples of a A-2-thiazoline-4-thione bearing a nonprotomeric group at C-2 are known. Some fused compounds are reported in Table 41. 

The benzofuroxtin [benzofurazan oxide, 3,4-benzo-l,2,6-oxa-diazole-2-oxide, or 2,1,3-benzoxadiazole-l-oxide (1)] ring system has been reviewed briefly on several occasions, notably by Kaufman and Picard,Boyer, and Behr. The mqst recent of these covers the literature until 1959, and since that date there have been many advances in the subject. This, we feel, justifies the field being covered once more, and its separation from the monocyclic 1,2,5-oxadiazole oxides—the furoxans. We consider also other furoxano-fused compounds in this chapter, subject to the limitation that the ring adjacent to the furoxan is aromatic and six-membered. 

The 4,.5-benzo-fused compound, 1,2-naphthofuroxan (24) was the first compound in the benzofuroxan series to be prepared the... 

Like tellurophene the fused compound forms 1,1-addition products with halogens (73BSF2468), but further bromination of such a 1,1-dibromo species gave 1,1,2-tribromobenzo[/>]tellurophene, which was able to be reduced to 2-bromobenzo[b]tellurophene. The 3-chloro and -bromo compounds were isolated following reaction of triphenylphosphine and the appropriate carbon tetrahalide with 2,3-dihydro-3-oxobenzo[b]telluro-phene (80BSB763). 

The site of dihydroxylation in heterocycles depends on the nature of the heteroaromatic system (Scheme 9.31) usually, electron-rich heterocycles like thiophene are readily biooxidized but give conformationally labile products, vhich may undergo concomitant sulfoxidation [241]. Electron deficient systems are not accepted only pyridone derivatives give corresponding cis-diols [242]. Such a differentiated behavior is also observed for benzo-fused compounds biotransformation of benzo[b] thiophene gives dihydroxylation at the heterocyclic core as major product, while quinoline and other electron-poor systems are oxidized at the homoaromatic core, predominantly [243,244]. 

A neat stereoselective synthesis of trans-fused tetrahydropyrano[3,2-c][l]benzopyrans involves treating salicylaldehydes with alk-4-en-l-ols and triethyl orthoformate. The selectivity is attributed to steric repulsion in the endo transition state, the precursor of the cw-fused compound <96CL889>. 

More advanced example The trans fused compound (13) was needed for a synthesis of some gclsemium alkaloids. Immediate Dlels-Aldcr disconnection is impossible as it would require an anhydride with a double bond in a five-membered ring. This would be fumarlc anhydride (14) but it does not exist. 

What is described as a domino Knoevenagel-hetero-Diels-Alder reaction , involving the reaction of the glucose-derived aldehyde 93 with a 1,3-dicarbonyl compound in presence of either proline or ethylenediammonium acetate, leads to the doubly annulated 5 6 6-fused compound 94 (Scheme 30) <2004S1150>. If the dicarbonyl compound is Meldmm s acid, however, the sequence is completed by spontaneous elimination of acetone and carbon dioxide from the Diels-Alder adduct, to give compound 95 <2005ASC1353>. 

Formation of the outer pyrimidine ring, by a different route, is also the final step in the synthesis of the benzothi-azolopyrimidopyrimidine 264 (Equation 82) <1997JIC818>, and similarly the outer six-membered ring is formed in the final step which leads to the thiadiazole-fused compounds 265 and 266 (Scheme 64) <1995RCB1957,1999RCB364>. 

The stereoselectivity of the thermal ring-closure of the dodecatrieneones 42 is determined by the nature of the remote group R. trans-Fused products 43 predominate over cw-products 44 and their ratio increases as R varies from MeO through Me to H (equation 29). If the reactions are catalysed by diethylaluminium chloride only fraws-compounds are formed. The homologues 45 behave similarly34. In contrast, the 7-azadeca-l,3,9-trienes 46 (X, Y = H2 or O) yield more of the cis- than the traws-fused compounds, regardless of the nature of X and Y (equation 30)35. 

A general synthetic route to p-lactam-fused enediynes (Scheme 2.321) has been successfully developed (848). When nitrone (771) was subjected to Kin-ugasa reaction conditions, two p-lactam containing products were obtained the elimination product (772) and the trans fused compound (773). 

There are two distinct classes of compounds that fit the criteria mentioned above alkene-functionalized chalcone derivatives (Fig. IB) and enone-functionalized chalcone derivatives (Fig. 1C). Within each class, both aromatic and non-aromatic compounds exist. Those compounds functionalized at the alkene include i) 3-membered heterocycles, e.g., epoxide and aziri-dine compounds, ii) 5-membered aromatic derivatives including fused and non-fused compounds, and iii) 6-membered aromatic pyrazine compounds. The enone-functionalized compounds include i) 5-membered aromatics such as pyrazole and isoxazole compounds, ii) 5-membered non-aromatic compounds for example pyrazolines and isoxazolines, and iii) 6-membered non-aromatics where a discussion of heterocyclic and non-heterocyclic compounds will be given for completeness. 

Finally, it is worth mentioning that 15N-NMR spectra of yohimbine (74), reserpine (109), and isoreserpine (514) also have been investigated (319). The 15N chemical-shift differences between C/D-cis- and trans-fused compounds could be explained by a hyperconjugative interaction between the antiperiplanar C—H bonds and the nitrogen lone pair characteristic for trans-fused compounds only. 

The model values selected from cyclohexane-fused compounds may give somewhat overestimated contributions to the Z-out conformation in cyclo-pent[e][l,3]oxazines and -thiazines. 

Table 1 lists monobenzo- and dibenzo-fused compounds (including cationic species) that were s mthesized by the methods given in Sections 2.4-2.8. 

This chapter covers literature published since 1982 early materials are included here only where needed as a basis for describing further developments or where not previously mentioned in CHEC-1 <84CHEC-l(5)669>. The structural types surveyed here include 1,2,3-triazoles, benzotriazoles, their dihydro derivatives and carbocyclic fused compounds. Compounds with heterocyclic fused rings are not included. The nomenclature system was discussed in CHEC-T <84CHEC-I(5)670>. 

Thietes are easily polymerized to different types of macromolecules that often turn up as undesired by-products. The fused compound 149 is easily transformed into a thioacrolein (Eq. 70), which polymerizes to a glassy solid. ... 

From a structural analysis of as- and /ra r-2-imino-l,3- and -3,1-perhydrobenzoxazines 92 and 93, it was concluded that all these /ra r-fused compounds exist in biased chair-chair conformations 92, as expected, whereas the m-fused 1,3-benzoxazines 93 (X = O, Y = NMe) attain exclusively the O-in conformations 93a. For the m-fused 3,1-benzox-azines 93 (X = NMe, Y = O), predominance of the N-out form 93b was found, owing to the favorable axial orientation of the A -methyl substituent <2003MRC435>. 

Acidic condensation of hydrazine with 3,4-diacyloxadiazole 75 was reported to give the pyridazine-fused compound 76 in high yield, as shown in Scheme 54 <2003T1059>. 

Padwa etal. utilized the ammonium ylide [1,2]-shift in the synthesis of tetrahydroisoquinoline and benzazepine fused with a five-membered ring, a structure found in a cephalotaxine family. When diazo ester 172 is treated with a catalytic amount of Cu(acac)2 in refluxing toluene, 5,7-fused compound 174 is isolated in 73% (Equation (25)). Again, use of Rh2(OAc)4 results in slow reaction and eventually gives a complex mixture of the products after a prolonged reaction time. 

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