Synthesis and Isomerization of Adducts of Azodicarbonyl Compounds and Cyclopentadiene

Abstract

The synthesis of a range of bicyclic Diels-Alder adducts (structures b) of cyclopentadiene with symmetrical and unsymmetrical azodicarbonyl compounds is described. Thermal isomerization of these adducts to the bicyclic 1,3,4-oxadiazines (structures c and d) is especially rapid with bulky acyl groups. In unsymmetrical adducts with acyl groups of markedly different size, the larger group dictates completely the direction of isomerization. Adducts with two different aroyl groups give both isomers.Spectroscopic properties of the adducts, the oxadiazines and the dihydro derivatives of the oxadiazines are described.La synthtse d'une gamme de composes d'addition bicycliques du type Diels-Alder (structures b) du cyclopentaditne avec des composes azo-dicarbonyles symktriques et non symttriques est dtcrite. L'isomtrisation thermique de ces composes d'addition en oxa-1,3,4 diazines bicycliques (structures c et d) est rapide sptcialement avec des groupes acylts volumineux. Dans les composts d'addition non symttriques avec des groupes acyles de taille nettement difftrente,'le groupe le plus gros impose complttement la direction d'isomkrisation. Les composts d'addition avec deux groupes aroyles difftrents donnent a la fois des isomtres.Les proprittts spectroscopiques des composts d'addition, les oxadiazines et les dtrivts dihydro des oxadiazines sont dtcrits. Canadian Journal of Chemistry 50, 371 (1972)We have recently shown (1) that the thermal isomerization of the cyclopentadiene adduct 16 (2) gives, as suspected (3), the racemic 1,3,4-oxadiazine derivative lc,d. The isomerization was cleanly first order, was relatively insensitive to solvent character, had a negative entropy of activation, and thus possessed all the features of a [3,3] sigmatropic process (4).We now wish to describe the synthesis and properties of a range of adducts from cyclopentadiene and azodicarbonyl compounds and of their thermal isomers. These include the achirall adducts 26-76 from symmetrically substituted azo compounds which give the racemates 2c,d-7c,8 and the chiral ones (one enantiomer shown) 86-126 from unsymmetrically substituted azo compounds, and from each of which potentially two structural isomers, 8c-12c and 8d-12d, can be expected.All of the azo compounds 2a-12a required for the present study were obtained by oxidation of the appropriate dicarbonylhydrazine with Nbromosuccinimide (NBS) in the presence of pyridine (5) or by oxidation of the mercury(I1) salt of the hydrazine with bromine (2). Only 3a, 7a, 9a, and 12a (6-9) have been previously 'On the basis of time-averaged conformational processes. 'Hereafter these will be designated simply as e.g. 2c.prepared as pure substances.The diaroyl azo compounds 2a, m.p. 155.5-157.5", 4a, m.p. 157", and 8a, m.p. 96-97" were all stable crystalline substances. None of the others could be isolated in crystalline form.There have been several attempts (9-13) to synthesize azodiacetyl, the simplest aliphatic azodiacyl, but in no case has the product been adequately characterized. Stolle (10) described...

1,2-Diphenyl-3,5-dimethyl-4-oxo-6,7-diazabicyclo[3.2.0]hept-2-ene, a nitrogen unsubstituted diazetidine with an unusually unreactive nitrogen

“…Its structure was inferred from its ir peak at 1680 cm-I and the symmetry in its 'Hmr spectrum. To check the possibility that the oxadiazine 9 might account for these spectra, with fortuitous shift equivalence of stereochemically unrelated protons, the synthesis was repeated., The uv spectrum of the product with a broad shoulder centred around 275 nm rigorously excluded structure 9 in which a strong band at 290-300 nm would be required (7). The 13Cmr spectrum also confirmed the equivalence of all the expected carbons in 8.…”

“…The ether layer was washed repeatedly with water, to remove the methanol, and then dried and evaporated to give nearly pure IOU. (15) mp 185-187"C), wasconvertedinto its mercuric salt (7). The salt (12g.…”

“…Attetnpted Ptrthaloylatiot~ of 7 Phthaloyl chloride (42mg, 0.2lmmol) and 7 (60mg, 0.21 mmol) were kept in pyridine (I mL) for 12 h. Evaporation, addition of water, and ether extraction led to an ether soluble fraction whose 'Hmr spectrum was extremely complex.…”

The formation and interconversion of oxazines and dioxazines from the reaction of nitrosocarbonyl compounds with cyclopentadienes

“…followed from their spectra. The 'Hmr spectra It was also shown not to be an artifact of the reaction resembled those of adducts from cyclopentadiene and conditions, since I d did not isomerize in the presence unsymmetrical azodicarbonyl derivatives, both in of N-bromosuccinimide-pyridine in methylene chlochemical shifts and in couplings (9). The carbony1 ride.…”

“…& the N-C and 0-C ring bonds are eclipsed, or nearly so, and the nitrogen atom is pyramidal, with a localized electron pair and an electron-withdrawing substituent (RCO). Theoretical calculations predict that this geometry is very near the potential energy maximum for the internal rotation of the N-0 bond (13,14) and this seems to be supported by spectroscopic evidence ( i [5][6][7][8][9][10][11][12][13][14][15][16][17].…”