Naphthalen-l,4,imines

Derivatives of the naphthalen-l,4 -imine ring system (2) have become available only since the discovery of cycloaddition reactions of benzyne, on the one hand, and the recent rapid development of isoindole chemistry on the other. 

White and M. E. Mann, Advan. Heterooycl. Chem. 10, 113 (1960), and references therein. 

4 -Dihydronaphthalen-1,4-iwmes from Isoindoles The naphthalen-l,4-imine derivatives 91-99 have been obtained by addition of acetylenedicarboxylic esters to the appropriate isoindoles. 3- ss Some such adducts react further with acetylenic esters (see Sections III, G and H), so that A -ethyl- and A-n-butylisoindole give 1 2 adducts with dimethyl aoetylenedicarboxylate instead. iV-Methylisoindole appears to be exceptional in giving an oily 2 1 adduct, for which structure (100) was suggested on analogy with the 2 1 adduct obtained from l,3-diphenylbenz[c]furan and acetylenedicarboxylic acid.  

The reactions of isoindoles with other acetylenic dienophiles have yet to be explored. 

i-Dihydronaphthalen-l,4i-imines from Pyrroles Although pyrrole itself and benzyne afford 2-phenylpyrrole, the Diels-Alder addition of benzyne to substituted pyrroles provides an alternative synthesis of naphthalen-l,4-imines (see Table II). 

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Use has been made of the C-N cleavage in the conversion of the bicyclic tertiary amines, derived from the 4tc + 2tc cycloaddition of pyrroles and isoindoles with benzynes, into aromatic systems, e.g. naphthalen-l,4-imines and anthracen-9,10-imines yield naphthalenes and anthracenes with the extrusion of the nitrogen bridge [24] in yields which are higher than those obtained by standard oxidation procedures. 

In the 7-azabicyclo[2.2.1]heptadiene series there is as yet no instance known of aromatization by deamination such as occurs with some naphthalen-l,4-imine and anthracen-9,10-imine derivatives (see Sections III, H and IV, D). On the other hand, a close parallel exists between those reactions and some instances of aromatization of bicyclo[2.2.1] structures by loss of a heavier heteroatom from the 7-position, e.g., 70 71. 1,2,3,4,5-Pentaphenylphosphole reacts with dimethyl acetyl-... 

It should be noted that the 1 1 adducts of benzyne with pyrrylmag-nesium iodide, and A -methyl- and iV-benzylpyrrole were isolated and characterized only as the hydrobromide (113), the methiodide (115), and the picrate of 102, respectively. The low yields of all these derivatives are due in part to further reactions of thenaphthalen-l,4-imines with benzyne (see Section III, F and G). Yields are better where the starting pjnrole has an electron-withdrawing N-substituent. Some analogous naphthalen-l,4-imines expected from 1,2,5-trisubstituted pyrroles apparently rearrange spontaneously to j3-naphthylamine derivatives under the conditions for their formation (see Section III, F). The related adducts 107 and 108 are formed from tetrahalobenzynes and N-methy Ipyrrole. 

Preliminary studies of nitrogen substituent inversion processes have been reported for several naphthalen-l,4-imine derivatives. The syn and anti invertomers of the A-chloroamine (117) equilibrate in solution to a mixture in proportion 3 2. The process can be followed kinetically by NMR spectroscopy starting from the pure anti compound the inversion is relatively slow ki = 2.6 x 10 sec at 23°), and the free-energy barrier to inversion is as high AF = 23.5 kcal mole ) as values found for inversion in aziridines. (A-Chloroaziridine derivatives, for which the energy barrier is even higher, have also been resolved into diastereoisomeric invertomers. )... 

Protonic acids and some other electrophiles cause the aromatization of naphthalen-l,4-imines and of derivatives of the related 1,4-epoxy-1,4-dihydronaphthalene ring system (126) to naphthalene derivatives (see Section III,F), and simple electrophilic addition to the 2,3-double bond has not been observed. Ring-opening of the ether (126) also occurs on addition of alkyl or aryl lithium reagents as a result of exo attack by the nucleophile at the 2-position. ... 

When l,4-dihydronaphthalen-l,4-imine (2) was first obtained via the hydrobromide (113), it was shown to react with phenyl azide to give an adduct (127). The analogous phenyl azide adduct (128) from compound 103 has been better characterized. Naphthalen-l,4-imines also add diazomethane across the 2,3-double bond, forming pyrazolines, e.g., 104 -> 129, two of which have been photolyzed to give the corresponding cyclopropane derivatives (130) with extrusion of nitrogen. ... 

With one exception, naphthalen-l,4-imines with a double bond between C-2 and C-3 are not known to dissociate thermally by either possible retro-Diels-Alder pathway (the reverse of reactions described in Section III, A, 1 and 2), and the enthalpy requirements for the formation of a benzyne or an acylic acetylene are doubtless unfavorable. However, the mass spectra of compounds 93-99 reveal one important fragmentation of the molecular ions to be loss of dimethyl acetylene-dicarboxylate, and another fragmentation pathway involves the formation of nitrilium ions MeC=NR and PhC=NR from 93-95 and 96-99, respectively. ... 

UV irradiation of the naphthalen-l,4-imines 104 and 105 promotes their isomerization to 3-benzazepine derivatives 139 and 140. Although no direct evidence was obtained to confirm the formation of azaquad-ricyclanes (138) as intermediates (see Section II,F), the extra strain associated with structure 138 and the extra benzenoid stabilization of the products 139 and 140 make it understandable that the thermal rearrangement of 138 should occur faster than that of 76 or 78. Analogous photochemical transformations are those of compound 106 to trimethyl 3-benzazepin-l,3,5-tricarboxylate, and of 1,4-epoxynaphthalenes to benzoxepin derivatives. ... 

Similar aromatizations of naphthalen-l,4-imines can be brought about by other electrophilic reagents, the end result being the formation of N-substituted a-naphthylamines. For example, the intermediate 145 is also attacked by benzyne to give A ,iV-diphenyl-a-naphthylamine... 

Surprisingly, in view of the preparation of 1,2,3,4-A-penta-substituted naphthalen-l,4-imines (109-112), the 1,4-iV-trisubstituted compoimds... 

Nitrogen-Bridged Six-Membered Ring Systems 7-Azabicyclo[2.2.l]hepta-2,5-dienes, Naphthalen-l,4-imines, and Anthracen-9,10-imines L. J. Kricka and J. M. Vernon, Adv. Heterocycl. Chem., 1974,16, 87-122. 

Azabicycio [2 2 1 ]-hepta-2,5-dienes, Naphthalen-l,4-imines and Anthracen-9,10-imines... 

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