Anthracenes aryne adducts

A closely related reaction is observed with chloromaleic anhydride (218), which gives the apparent aryne adduct 216 with tetracyclone (151) but stops at the Diels-Alder adduct 219 with other dienes such as cyclopentadiene (146b), butadiene (146e), and anthracene (147). Not only does this result suggest the absence of an elimination-addition mechanism via the aryne (23) in this system. 

As in the case of the corresponding anhydride (23) (Section III.1.C), didehydromaleimide (30) probably does not qualify as a true aryne, but is expected to be sufficiently similar in properties to be covered in this review (Section I.2.C). This species (30) was first suggested as an intermediate along with the 1,2-dithiete (274) in the decomposition of the dithiin (275) in pyridine at 120°C to explain the formation of the aryne trimer (276). When this reaction was carried out in the presence of cyclopentadiene (146b), however, the failure to obtain the appropriate aryne adduct (277) was rationalized as being due to its presumed instability. The only products obtained from this reaction, as well as from butadiene (146c) and anthracene (147), were Diels-Alder adducts such as 278 and 279 of the dithiin (275) and the dithiete (274), respectively. 

The claim for this aryne is based on the isolation of the appropriate adducts 631 or 632 when a crown-ether complex of the diazonium carboxylate potassium salt 633 is decomposed in the presence of tetracyclone (151) or the diphenyltetrazine (169). As pointed out in Section II.2.B.C, however, both of these diene traps may be ambiguous as aryne probes because of their tendency to react with the aryne precursors by an addition-elimination process via 634 and 635 rather than by an elimination-addition mechanism involving the aryne 617. The failure of several other dienes with unambiguous records as aryne traps (Section II.2.B.b.d), such as anthracene (147), to give aryne adducts with the precursor 633 tends to support the former mechanism. On the other hand. 

In the context of this section it is important that Ruchardt and Tan (1970 a) found that (solid) benzenediazonium fluoroborate gave benzyne adducts with potassium acetate in the presence of aryne trapping agents such as tetracyclone or anthracene. This is, however, not the case if water is present (Cadogan, 1971). As a consequence of these observations, Cadogan et al. (1971) simplified the formation of arynes from diazonium ions by converting aniline or its substitution products into arynes in a... 

Bis-arynic reagents in which the two arynes are in separate, insulated arene rings have also been developed. For example, bis-anthranilic acid 478 is a synthetic equivalent for diaryne 479 aprotic diazotization of 478 in the presence of various dienes (i.e., tetraphenylcyclone, 2,5-dimethylfuran, anthracene) gave the expected bis-adducts in 40-... 

The formal Diels-Alder adduct (228) of anthracene and didehydromaleic anhydride (23) was subjected to flash vacuum thermolysis at 600°C in the hope that a retro-Diels-Alder reaction (Section II.1.E) might generate the aryne 23. Although the theoretical yield of anthracene was obtained, the aryne 23 could not be frozen out or indirectly detected by trapping experiments the only other identifiable products were CO and which could have arisen directly... 

Even stronger evidence for the existence of the aryne 26 has been obtained from the recent isolation of the actual Diels-Alder adducts 479 when the diazonium carboxylate (480) is decomposed in the presence of various anthracenes (147). This discovery of a solution phase method for apparently generating the aryne 26 is significant beyond its use as a source of the difficultly accessible heterotriptycenes such as 479. In particular, it should... 

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