Benzyne additions

Benzyne, generated either by oxidation of 1-aminobenzotriazole with lead tetraacetate or by decomposition of benzenediazonium-2-carboxylate, was efficiently trapped by (2) to give 88% of the 1,2-benzisoselenazole (26) however, it was trapped in only 5-10% yield by (1). The series of adducts analogous to (26), prepared from benzyne and substituted benzoselenadiazoles (81JCS(P1)607), occurred via attack of the benzyne at the selenium atom followed by reorganization of the intermediate according to Scheme 6. Benzyne addition to dimethylthiadiazole produced methyl derivatives of quinoline and 1,2-benzisothiazole (82CC299). 

Manganese(m) acetate oxidation (cf. Vol. 3, p. 34) of camphene gives (186) as a 95 5 mixture by carboxymethyl radical insertion no rearranged products were obtained, in contrast to /3-pinene which gave Wagner-Meerwein products only, and no free-radical insertion.279 The E- and Z-isomers of (187) probably result from a non-concerted biradical intermediate formed by benzyne addition to camphene.280 Benzyl-lithium adds to the aminocamphor (188) exclusively from the exo-side whereas only the competing enolization reaction occurs with more sterically hindered organometallics.281... 

We speculated that the electron-withdrawing nature of the pyridine ring was responsible for the lack of reactivity of 23 toward benzyne. In troubleshooting the benzyne addition we examined the use of a methoxy group to offset the electron-withdrawing properties of the pyridine. Compounds 24-28 (Fig. 8) were prepared in the order indicated. As each was... 

Compounds 64 and 65 act as 1,3-dipoles and undergo cycloaddition with arylisocyanates and benzyne. Addition of arylisocyanates yields arylaminoquinoxalinones, and addition of benzyne gives o-hydroxy-phenylquinoxalinones (Scheme 17). ... 

Benzyne addition to fulvenes 191 also occurs exclusively from the endo face , but when the 1-carbon bridge in 188 is expanded to a 2-carbon bridge, as in 193, cycloaddition of benzyne is less stereoselective and exo attack predominates (195 194 = 81 19), a result which is contrary to what might have been predicted on steric grounds . In all of these studies on Ti-facial selectivity, benzyne was generated via the benzenediazonium carboxy-late route. 

A novel example of this reaction is the double benzyne addition to cyclopropenone 235 to give 236, an intermediate en route to the novel tritriptycyl cyclopropenium cation. ... 

Aryne cycloadditions have been coupled with radical cyclizations to rapidly assemble multiring systems For example, benzyne addition to furan 278 followed by radical cyclization onto the newly formed double bond gave 280 in two steps and fair yield. 

Benzyne (from anthranilic acid) cycloadds to mesoionic pyrimidines 320 the adducts 321 were obtained in 42-62% yields. Examples include R = Ph or CH2Ph, R = Ph or CH3 and R = alkyl or CH2Ph. Thermal decomposition of 321 (70-210°C depending on substitution) gave near-quantitative yields of isoquinolones 322. If the initial benzyne addition is conducted at elevated temperatures and if phenyl isocyanate elimination from the initial adduct 321 occurs at relatively low temperatures, then benzyne cycloadducts of the isoquinolones may also be formed (cf additions to 312). 

A monoadduct of C70 was also formed, but its structures as well as those of bis- and higher benzyne adducts of 50 remain to be determined. Also, there were indications that another monoadduct of 50 may also be formed under certain benzyne addition conditions . ... 

The other product could come from chlorination, elimination to give a benzyne, addition of amide anion to put the anion ortho to MeO (p. 524 in the textbook) and protonation. 

Benzonorbornadienes and Related Benzopolycyclics.—Cycloaddition routes to benzopolycyclics have been extended by investigations, which show the synthetic importance of [4 + 4] photocycloaddition, and by further examples of [4 + 2] thermal cycloaddition. Addition of dimethyl acetylenedicarboxylate to 2-substituted anthracenes provides a satisfactory route to substituted dibenzobarrelenes. Increasing methyl substitution in a series of polymethyl-naphthalenes facilitates Diels-Alder addition of maleic anhydride, "" and as expected the kinetically favoured product is the endo-addact but the thermodynamically favoured product is the exo-adduct. Details of the preparation of (347) by a benzyne addition and of further additions of dimethyl acetylenedicarboxylate to substituted naphthalenes are given.In order to investigate their conformational equilibria, (348) and (349) were synthesized by [4 + 2] cycloaddition of benzocyclobutadiene to 2,7-dimethylanthracene and by [4 + 4] cycloaddition of o-xylylene to 2,7-dimethylanthracene, respectively. The estimated barrier to inversion in (349) is 8 kcal mol . ... 

Benzyne addition to bicyclobutane to give (376) is considered to be a non-concerted process. 

Scheme 12 Modification of calix[4]furan 1 and its derivative 75 via benzyne addition [52]...

---