Benzene 1-5 ring closure

Subsequent studies reveal that excellent yields (70-95%) of 3-ethylanthranils are also obtained by reducing the o-nitrosopropiophenones with warm sodium bisulfite solution.153 With dry hydrogen chloride in an inert solvent (e.g., benzene) ring closure of 130 (R1 = R2 = H) is accompanied by... 

Azetidin-2-one formation by N—C(4) ring closure has also been observed in the irradiation of cfs-a-phenylcinnamides (143) in degassed benzene. Both cis and trans lactams are formed (68JA2333). 

A similar mechanism operates in the reaction of 3,3,3-trifluoropropene with benzene and aluminum chloride [12 13] Perfluorophenylpropene undergoes intramolecular electrophilic attack m a rare example of ring closure at a C -F bond [14] (equation 11)... 

The relative ease of preparation of condensed thiazole derivatives is a consequence of facile thiazole ring closure, and therefore also benzothiazole amines with an amino group on the benzene ring (except for the weakly regioselective nitration of benzothiazoles) are very easily accessible and useful substrates for the Gould-Jacobs reaction. 

More recently, a double reductive ring closure of the dinitrodiphenylbenzene 139 with triethyl phosphite as the reducing agent has been reported to produce 3 in 59% yield (Scheme 18). The precursor 139 was prepared in excellent yield by Pd(0)-catalyzed coupHng of phenylboronic acid and 1,3-dibromo-4,6-dinitro-benzene (92JHC1237). 

The diazo function in compound 4 can be regarded as a latent carbene. Transition metal catalyzed decomposition of a diazo keto ester, such as 4, could conceivably lead to the formation of an electron-deficient carbene (see intermediate 3) which could then insert into the proximal N-H bond. If successful, this attractive transition metal induced ring closure would accomplish the formation of the targeted carbapenem bicyclic nucleus. Support for this idea came from a model study12 in which the Merck group found that rhodi-um(n) acetate is particularly well suited as a catalyst for the carbe-noid-mediated cyclization of a diazo azetidinone closely related to 4. Indeed, when a solution of intermediate 4 in either benzene or toluene is heated to 80 °C in the presence of a catalytic amount of rhodium(n) acetate (substrate catalyst, ca. 1000 1), the processes... 

Benzene-1,2-diamine or derivatives are generally employed as the diamino component in ring-closure reactions with 1,2-dicarboxylic acids or derivatives (Table 2). 

Most of the required. vy/ -benzene dioxides are prepared by epoxide ring-closure reactions of appropriate precursors, e.g. 7, 9 and io.6-8-11-13... 

Shortly before this work by Pschorr, similar ring closures had been described for other compounds in which two benzene rings are already linked. Thus Graebe and Ullmann (1894) found that 2-diazobenzophenone can be converted into fluorenone in the analogous manner (Scheme 10-74). Similarly, when Staedel (1894) added nitrous acid to 2,2 -diaminobenzophenone he obtained some 1-hydroxyfluorenone. The ring closure of 2-benzylbenzenediazonium ion to give fluorene (Scheme 10-75) was described by Fischer and Schmidt (1894). 

The 10 OC route was followed for the synthesis of tetrahydrofurans possessing a y-amino alcohol moiety 247 (Eq. 29) 118]. Aldoximes 21a-f (see also Eq. 3 and Table 2), when heated in benzene in a sealed tube at 110 -120 °C for 6 h, underwent smooth intramolecular cycloaddition to the tetrahydrofuranoisoxazo-lidines 246a-f in 70-83% yield (Eq. 29). This ring closure proceeded stereo-specifically to generate three adjacent stereogenic centers. LAH reduction of 246 b resulted in isolation of stereospecifically functionalized tetrahydrofuran derivative 247b in 75% yield. 

The spiroindolinobenzopyran 2 is a classical example of spiropyran and is easily prepared by the condensation of l,3,3-trimethyl-2-methyleneindo-line (Fischer s base) and salicylaldehyde in anhydrous ethanol or benzene (Scheme 2).ia The nucleophilic attack of Fischer s base on the carbonyl group (like an enamine) gives an aldol product, which undergoes ring closure followed by dehydration. This condensation is reversible therefore, an exchange of the salicylaldehyde component of spiropyran with a different salicylaldehyde is possible. For example, when a solution of spiropyran 2 (Scheme 2) was refluxed with 3,5-dinitro-substituted salicylaldehyde, the open form of 6,8-dinitro-BIPS was obtained.2... 

Ring closure between an adjacent pair of aromatic substituents is also possible an example is the formation of indan from l-methyl-2-ethyl-benzene 11,109). In fact, Csicsery 109) found that the rate of cyclization of l-methyl-2-ethylbenzene to indan over platinum was somewhat faster than that of n-butylbenzene to methylindan, indicating that kinetically there is nothing to be gained by having ring closure at an aromatic carbon... 

The metal-catalysed olefin metathesis (equation 122) when applied to dienes results in ring-closure and expulsion of an olefin (equation 123). Thus the molybdenum carbene complex 241 promotes the decomposition of the 1,6-heptadiene derivative 242 to a mixture of the cyclopentene 243 and ethylene (equation 124)122. An analogous reaction of the alcohol 244 gives 245 (equation 125), and 4-benzyloxy-l,7-decadiene (246) affords the cyclohexene 247 and 1-butene (equation 126). These transformations, which occur in benzene at room temperature, proceed in excellent yields122. 

The reaction of 220 with primary alkylamines in benzene yielded, after ring-closure, the novel heterocycles 222. It was assumed that 220 reacted with primary amines to first yield the corresponding 3-amino derivatives 221 which subsequently added to the carbonyl group to give the ring-closed aminal 222 <00JHC1299>. 

Activity in the area of medium effects (27) has declined greatly in recent years, though there has been some interest in kinetics and mechanisms in supercritical fluids (28). Indeed activation volumes for ring closure reactions of diimine-carbonyls M(CO) (diimine) show some of the most dramatic medium effects. Thus AF values range from +66 to +4 cm3 mol-1 on going from 7% benzene in supercritical C02 (at 35 °C) to 100% benzene (at 25 °C) (29). 

Ring closure of triazinyl diester 276 was reported by Moderhack etal. <2002M1165>. This compound was treated with hydrazonoyl chloride in the presence of triethylamine in refluxing benzene. Formation of the intermediate 277 was anticipated, which, upon intramolecular cyclization, afforded the fused triazole 278 in medium yield (42%). Syntheses of other related compounds via modified synthetic routes have also been described. 

Acidic ring closure resembles the Du Pont process in that the central benzene ring of the quinacridone structure is synthesized totally. The process bears resemblance to the Liebermann method [2, see also 1.3]. Condensation of succinylosuc-cinic ester with two equivalents of arylamine affords 2,5-diarylamino-3,6-dihy-droterephthalic diester. Subsequent oxidation with suitable agents yields 2,5-di-arylaminoterephthalic diester 57. Hydrolysis and cyclization in polyphosphoric acid or other acidic condensation agents produces crude quinacridone [10]. This product already consists of very small particles. 

The ring closure of A-(3-chlorophenyl)aminomethylenemalona-mate (781, R = Cl) and the 4-chloro derivative in boiling benzene on the action of phosphoryl chloride for 6-10 hr afforded the corresponding 4-(arylamino)quinoline-3-carboxylate (e.g., 783) in 57-65% yield... 

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