Azonines

Azonine, 1-phenylsulfonyl-AGL , AHLrr, ASL , 7, 723 <72AOR281) Azonine, potassium salt... 

Azonine-l-carboxylic acid, 4,5-epoxy-, ethyl ester AGi,. , 7, 724 <77JA2651>... 

Pyridazine 1-oxide N NMR, 2, 17 <80HCA504) Pyridazino[4,5-d]azonine-7-carboxylic acid, 1,4-dipbenyl-, etbyl ester... 

Anastassiou has summarized in two reviews the knowledge about IH-azonine (41a) [72ACR281 78AHC(23)55]. Compound 41a as well as its salts (N M" ) are aromatic compounds which exist as such and not as imine polyenic forms. Tliis compound demonstrates a valence isomerism 41a/41b similar to that of l//-azepine (14a/14c see Section II,A,1) the transformation 41a 41b occurs upon irradiation. 9-Azabicyclo[6.1.0]nona-2,4,6-triene 41b displays no tendency to thermal isomerization to 41a at ambient temperature (72ACR281). 

Oxonin (1, X = O) has polyenic character, is heavily buckled and is thermally rather unstable. Azonines 1 (X = NR) incorporating electron-withdrawing groups R on nitrogen are also uniformly characterized as olefinic compounds They are thermally labile and are decidedly atropic according to their spectroscopic data. 

Azonine anions 1 (X = N M + ), the parent compound 1 (X = NH) and, to a lesser extent, alkyl-substituted derivatives (X = NR), however, can be classified as aromatic, as they are flat, display high thermal stability and exhibit diatropic properties. 

A general entry into the azonine system, c.g. 4, is by photoinduced electrocyclic ring opening of the bicyclic valence isomer 3,9 11-13 which is readily prepared by earboethoxynitrene addition to cyclooctatetraene. 

Ethyl azonine-l-carboxylate (3) can be used to prepare the parent 1//-azonine12 (1, R = H). as well as a number of substituted systems via its anion 213 (vide supra). 

Synthesis with Retention of the Azonine Ring System i) By Exchange of A -Substituents... 

The anion 11 which is readily formed on low temperature exposure of 4 to potassium lert-butoxide can be used to prepare a rich variety of A -substituted azonine systems 1 by trapping with appropriate electrophiles (RX).9,12... 

Different derivatives of the benzannulated azonine can also be prepared via the generation of an anion, generated from 8 with methyllithium.14 ... 

During the period 1976-1986, biosynthetic studies on hasubanan alkaloids were carried out by Battersby et al. (81-84) for hasubanonine (5) together with protostephanine (57). The two alkaloids, isolated from Stephania japonica, arise from the same precursor, and their unusual structures are of biosynthetic interest, namely, the vicinally trioxygenated ring C in 5 and the unique natural example of a dibenz d,f ] azonine skeleton in 57. 

The first synthesis of 9-azabicyclo[6.1.0]nona-2,4,6-triene (235) has been achieved by irradiation of l//-azonine (236) at 0°C.179 An oxonin structure (237) has tentatively been assigned to the labile photoproduct of the azonine 1,2-oxide 238.180... 

Many other miscellaneous additions of alcohols have been described. Polar addition of methanol to 2//-pyrroles264 and to azepines265 has been observed. Photoaddition of methanol to the 1,3,4-oxadiazole 320 is followed by cycloelimination of methyl benzoate (321) to give the ylid 322.266 An adduct (323) of the ylid and the 1,3,4-oxadiazole has been isolated. Photoaddition of methanol to the quaternary ammonium salt 324 results in ring expansion and the formation of the azonine 325.267... 

PE. Evans u. A.B. Holmes, Tetrahedron 47, 9131-9166 (1991) Medium-Ring Nitrogen Heterocyclcs" (Azepines, Azocines, Azonines, and Derivatives). 

In terms of simple Hiickel theory the change from polyenic to aromatic the system experiences on passing from (1) and (2) to (3) was attributed primarily to the lower LVMO energy of the latter (B-73MI52000). A more detailed Hiickel calculation (72T3657) utilizing properly selected models in conjunction with thermochemical data also correctly accounts for the differences in tt-electron makeup between 1/Z-azonine (3a) and oxonin (1), which... 

A further group of monoannulated heteronins is represented by the three oxygen-bridged azonines (10), (11) and (12) (77JOC2651). They are all characterized by UV absorption at ca. 270 nm and NMR (1H, 13C) data consistent with the presence, nature and location of the oxygen bridge and double bonds indicated in each case. 

Utilization of suitably structured dienes (101) and (102) leads to efficient cycloadditive interception of fleeting mono-trans azonine rotamers (86) and (87) to yield trans fused cycloadducts (103) (73JOC1959) and (104) (73TL3805), the specific diastereomeric arrangement depicted in (103) having been deduced from X-ray crystallographic data (73JOC1959). 

---