Imino annulene

The preparation of l,6-oxido[10]annulene, described simultaneously by Sondheimer and Shani4 0 and by Vogel, Biskup, Pretzer, and Boll, is illustrative of the rather general synthesis of aromatic 1,6-bridged [10]annulenes starting from 1,4,5,8-tetrahydronaphthalene. Apart from the present compound, the following bridged [10]annulenes have thus far been obtained by this approach l,6-methano[10J-annulene,2-8-9 the ll,ll-dihalo-l,6-methano[10]annulenes,9 10 and 1,6-imino [ 1 OJannulene.11... 

Of particular interest is the syn-l,6-imino-8,13-methano[14]annulene (59) which represents the first authenticated example of a stable 1H-azepine with a free NH group (80AG(E)1015). The annulene with aluminum oxide undergoes a remarkable isomerization to the anti isomer (61). Investigation shows that the isomerization is not a thermal reaction but involves alumina-catalyzed proto tropic shifts via the 3/7-azepine tautomer (60). This system is unique in that it is the first example of a 3H -> 1H azepine tautomerism, and is a consequence of the high degree of strain in the anti-Bredt 3iT-azepine (60). 

On flash vacuum pyrolysis the l,6-imino[10]annulenes (62 R = Me, Me3Si, C02Me) isomerize to the 1H-1 -benzazepines. 

The present review includes hydrazino- and imino-bridged annulenes with internal nitrogen atoms coplanar with the peripheral atoms of the system. The literature is covered to the end of 1975, with some later references. 

When l,6-imino-10-annulene (68) is oxidized with singlet oxygen and the product is thermolyzed, the homobenzene derivative 69 is formed. This, on treatment with nitrosyl chloride in the presence of triethylamine gives 25 in 5% yield.38 Also, annulene 70 on treatment with bromine gives the dibromoarene... 

The nearly planar structure of Pd(II) complex 123 enabled a twofold connection of the bicyclic units in imino ether condensations brought about by Meerwein s salt and diisopropylethylamine in methylene chloride. Protonation of 124 (Scheme 14) generates a Pd(II) complex (125) of an octahy-droporphyrin, with complete saturation of the peripheral double bonds containing the 7t-system of l,5,9,13-tetraaza[16]annulene (68AG622). 

Should one ask for direct enthalpy of formation investigations on anti-Bredt enamines, such studies are currently limited to l,6-imino[10]annulene (14) with its gas phase enthalpy of formation of 367.2 7.0 kJ mol-1. How do we affirm the decrease in resonance energy accompanying its geometric constraints There are no enthalpy of hydrogenation measurements for this compound, nor for any other 11-azabicyclo[4.4.1]-undecane (30) derivative71. However, we do know the gas phase enthalpy of formation... 

Annulene Imino-oxide-sulfide (2.344) Aromatic Aromatic 117... 

Direct reduction of naphthalene 1,4-quinone with diisobutylaluminum hydride produces the free cis-1,4-dihydrodiol. C -naphthalene dioxide 153 and compound 158 have been obtained by the photooxidation of l,6-imino[10]annulene, followed by thermal isomerization and reaction with nitrosylchloride. An inter-... 

These few typical examples (41 to 48) indicate the dramatic effects operating in these systems, where the meso protons resonate about 5 ppm downfield from normal olefinic protons, and the imino protons, even when attached to a positively charged nitrogen atom, are shifted to very high fields. This behaviour is indicative of a substantial diamagnetic ring current in these molecules and lends credence to their inclusion as bridged [18]annulenes. 

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