Allenic hydrazones

Pyridazines were obtained also by photolysis of 1-phenyl-l-vinyl azide in the presence of iron pentacarbonyl (3,6-di-phenylpyridazine was obtained in 1.1% yield) (78HCA589) or by thermal decomposition of an allenic hydrazonate (81JA7011). Acetylenic hydrazides can be transformed into pyridazines [84BSF(2)129], and thermal cyclization of dialkali metal salts of cu-hydroxyketone tosylhydrazones afforded pyridazines in moderate yield (85TL655). Propionyl phenylhydrazine, after reaction with 4-bromobutyronitrile, converts into a pyridazine (87SC1253). 

Allenic hydrazones undergo a gold(I)-catalyzed cycloisomerization to substituted pyrroles, which are obtained with excellent yield (Scheme 4-60). This transformation requires heating of the allene with PhaPAuNTf-toluene complex in dichloromethane to 100 °C for 20 min. A 1,2-alkyl or aryl shift is key to the formation of the aromatic heterocycle. 

A number of reaction pathways have been proposed for the Fischer indolization reaction. The mechanism proposed by Robinson and Robinson in 1918, which was extended by Allen and Wilson in 1943 and interpreted in light of modem electronic theory by Carlin and Fischer in 1948 is now generally accepted. The mechanism consists of three stages (I) hydrazone-ene-hydrazine equilibrium (II) formation of the new C-C bond via a [3,3]-sigmatropic rearrangement (III) generation of the indole nucleus by loss of... 

Whereas the reactions of allenephosphonates 171 (R2 = OEt) with primary aliphatic and aromatic amines 172 and the reactions of the phosphane oxides 171 (R2 = Ph) with aliphatic amines 172 afford the conjugated addition products 173 always in good yields, the addition of anilines to 171 (R2 = Ph) leads to an equilibrium of the products 173 and 174 [231]. However, treatment of both phosphane oxides and phos-phonates of type 171 with hydroxylamines 172 (R3 = OR4) yields only the oximes 174 [232, 233]. The analogous reaction of the allenes 171 with diphenylphosphinoylhy-drazine furnishes hydrazones of type 174 [R3 = NHP(0)Ph2] [234],... 

Electron-deficient allenes also undergo hetero-Diels-Alder reactions. N,N-Dimethyl-hydrazones 193 reacted with allenedicarboxylate 110a in refluxing acetonitrile to give 2-carboxy-3-pyridineacetic acid diesters [157]. 

The addition of a-lithiomethoxyallene 144 [55] to benzaldehyde dimethylhydra-zone 145 (Eq. 13.48) leads to a mixture of pyrroline 146 and dihydroazete 147 [56]. The cydization in this case, which takes place in the same operation as the addition to the hydrazone, follows two distinct pathways, with attack of the nitrogen atom taking place at the inner, in addition to the terminal, carbon atom of the allene. A similar reaction of 144 with SAMP-hydrazone 148 (Eq. 13.49) leads to 3-pyrroline 149 in 88% yield and excellent diastereoselectivity [57]. Cleavage of the chiral auxiliary group from 149 takes place in two steps (1, methyl chloroformate 2, Raney nickel, 50 bar, 50 °C) in 74% overall yield. When the addition of 144 to 148 is conducted in diethyl ether, cydization of the adduct does not take place. Surprisingly, the hydrazones of aliphatic aldehydes react with 144 in poor yield in THF, but react quantitatively and diastereoselectively in diethyl ether to give the (uncyclized) allenyl hydrazone products. 

Bicyclo[3.1.0]hex-2-en IV/3, 130f. (Cyclopropanier ) V/lb, 709 (aus dem Hydrazon) E19b, 232 (Bamford-Stevens-Reaktion), 543 (Hydrazon-Spaltung) Bi-cyclopropyliden E19b, 198 (Carben + Allen) E17b, 1443 ( —HBr) Cyclobutadien 1,2-Dimethyl-(f/4-Dichloronickel-Komplex) IV/4, 243... 

The postulate that ethylidene is formed in this system rests on an analogy with its presence in the photolysis of diazoethane - and also by analogy with the similarity of the products produced by the photolysis and pyrolysis of other diazirines and by the decomposition of tosyl-hydrazones, which are thought to involve carbene intermediates. Attempts were made to detect ethylidene (by its addition reactions) by photolyzing methyldiazirine in the presence of large excesses of ethylene, propylene, and allene. In no case was any product detected that could be ascribed to the addition of ethylidene to any of these molecules. 

The hydrazone 364 of 3-thietanone reacts with hydrogen sulfide to give the dispiro derivative 384. Thermolysis of the sodium salts of p-toluenesulfonyl-hydrazones of 3-thietanone,2,2,4,4-tetramethyl-3-thietanone and 2-isopropylidene-4,4-dimethyl-3-thietanone yields allene or cumulene epi-sulfides, for example, 385. The reactions of some tris-iminothietanes are discussed in Section XV.3.B. ... 

Allene episulfide and butatriene 2-episulfide are formed by thermolysis of the lithium tosyl-hydrazone of thietan-3-ones (Scheme 80) <76JA708l, 81TL4815). 

A novel method of preparing tetramethylallene is by cycloelimination from 3,3,5,5-tetramethyl-l-pyrazolin-4-one hydrazone, which occurs on treatment of this compound with an excess of nickel peroxide at room temperature, yielding nitrogen and 87-91% of the allene 163... 

Semi-empirical INDO calculations have been carried out on cycloheptatrienyli-dene, cycloheptatetraene, and related systems. The most stable structure for cyclo-heptatetraene was found to be non-planar with a C2 axis of symmetry, and should be more stable than the carbene form. Even though most of the chemistry of cyclo-heptatrienylidene is consistent with carbene behaviour, the allene and carbene forms may be in equilibrium, and the position of equilibrium solvent-dependent. In fact decomposition of the sodium salt of the toluene-p-sulphonyl-hydrazone (163) gives dimeric products formed from allene (164), and addition of cycloheptatrienylidene to tetracyclones gives products derived from the adduct (165). ... 

An efficient procedure for the synthesis of 2-pyrazolines from unsaturated hydrazone derivatives obtained from allenic phosphine oxides and acethy-drazide or benzhydrazide was described. ... 

The hydrazone (CFs)jCH-C( N-NHa)-CH(CFs)j has been obtained in low yield by treatment of tetraki (trifluoromethyl)allene with hydrazine in ether at 0—5 °C. ... 

S-Alkylthiosulfates s. S-Carb-amylmethylthiosulfates Allenes, diene synthesis with — 16, 733 Alloxan 5-hydrazones 16, 460... 

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