Hydrogenation diimide

Aikenes are usually reduced by catalytic hydrogenation. Diimide reduction is a mild and neutral alternative. Keith R. Buszek, now at the University of Missouri, Kansas City, has shown J. Org. Chem. 2007, 72, 3125) that the reduction can conveniently be carried out on resin-bound aikenes, using 2-NBSH (o-nitrobenzenesulfonyUiydrazide) with Et N for convenient room temperature diimide generation. 

Dia ene deductions. Olefins, acetylenes, and azo-compounds are reduced by hydrazine in the presence of an oxidizing agent. Stereochemical studies of alkene and alkyne reductions suggest that hydrazine is partially oxidized to the transient diazene [3618-05-1] (diimide, diimine) (9) and that the cis-isomer of diazene is the actual hydrogenating agent, acting by a concerted attack on the unsaturated bond ... 

The available studies indicate that diimide has been used as a reducing agent for the preparation of HNBR. It has been used mainly as an alternative for hydrogenation of nitrile rubber latex. The use of diimide to hydrogenate low-molecular weight olefines is well known in the organic literature [93]. Diimide can be conveniently generated in situ by thermal treatment of solutions of p-tolu-enesulfonyl hydrazide or oxidation of hydrazine. 

The addition is therefore stereospecifically syn and, like catalytic hydrogenation, generally takes place from the less-hindered side of a double bond, though not much discrimination in this respect is observed where the difference in hulk effects is small.Diimide reductions are most successful with symmetrical multiple bonds (C=C, C=C, N=N) and are not useful for those inherently polar (C=N, C=N, C=0, etc.). Diimide is not stable enough for isolation at ordinary temperatures, though it has been prepared as a yellow solid at — 196°C. 

Catalytic hydrogenation transfers the elements of molecular hydrogen through a series of complexes and intermediates. Diimide, HN=NH, an unstable hydrogen donor that can be generated in situ, finds specialized application in the reduction of carbon-carbon double bonds. Simple alkenes are reduced efficiently by diimide, but other easily reduced functional groups, such as nitro and cyano are unaffected. The mechanism of the reaction is pictured as a concerted transfer of hydrogen via a nonpolar cyclic TS. 

Reduction by diimide can be advantageous when compounds contain functional groups that would be reduced by other methods or when they are unstable to hydrogenation catalysts. There are several methods for generation of diimide and they are illustrated in Scheme 5.4. The method in Entry 1 is probably the one used most frequently in synthetic work and involves the generation and spontaneous decarboxylation of azodicarboxylic acid. Entry 2, which illustrates another convenient method, thermal decomposition of p-toluenesulfonylhydrazide, is interesting in that it... 

Beton and co-workers extended the hydrogen bonding approach to two-component systems, generating a number of structures that utilise different molecular motifs.24 26 In the case of perylene tetracarboxylic diimide (PTCDI) co-adsorbed with melamine (1,3,5-triazine-2,4,6-triamine) on a silver-terminated silicon surface, a network is formed in which the straight edges correspond to PTCDI with melamine at the vertices (Figure 11.6). The network shows large-area pores that the authors used to trap heptamers of C6o molecules. 

It was envisioned that hydrindanone 83 and cyclopentene 85 could be used as intermediates in the synthesis of e f-retigeranic acid A (1) and e f-retigeranic acid B (2), respectively. To prepare the building block 90, cyclopentene 85 was reduced with diimide (93 %) in order to prevent isomerization and subsequently deprotected with PPTS to yield hydrindanone 90 (quant.), which could provide access to <77/-retigeranic acid B (2) (Scheme 10.7). Hydrindanone 83 was reduced via an enol triflate and then subjected to Pd-catalyzed reduction to provide cyclopentene 91 (87 % from 83). Upon hydrogenation of 91 with Pd/C and cleavage of the acetal with iodine, protected hydrindanone 92 (95 % from 91) was obtained. The deprotection of 92 provided ent-60, whose enantiomer was used in previous syntheses of retigeranic acid A (1) by Corey [14] and Hudlicky [46, 47]. 

Transfer of hydrogen occurs exclusively in a syn manner and it has been concluded that the reduction of a multiple bond by diimide involves a synchronous transfer of a pair of hydrogens to a single face of the carbon-carbon double bond via a six-membered cyclic transition state to give a syn adduct (equation 22)77,81. 

Diimide can act as both a hydrogen acceptor and donor, undergoing disproportionation as a side-reaction which produces a considerable amount of nitrogen gas. From a practical point of view the occurrence of this disproportionation reaction requires the use of an excess of the diimide precursor. 

The superfluous carbonyl oxygen atom was removed by carbonyl reduction to provide the alcohol 171, subsequent Chugaev elimination (via 172 to 173) and double bond hydrogenation with in situ generated diimide (Scheme 27) [94]. The isopropenyl double bond was finally re-established by reductive cleavage of the a-bromo ether unit in 173 to afford the fully functionalized enantiomerically pure A-ring building block (162). 

Diimide diimine, diazene), N2H2 or HN=NH, is an ephemeral species which results from decomposition with acids of potassium azodicarboxylate [264, 265] from thermal decomposition of anthracene-9,10-diimine [266, 267], and of hydrazine [268,269] and its derivatives [270]. Although this species has not been isolated, its transient existence has been proven by mass spectroscopy and by its reactions in which it hydrogenates organic compounds with concomitant evolution of nitrogen [271]. 

The behavior of dienes and polyenes - both open chain and cyclic - toward reduction depends especially on the respective positions of the double bonds. Carbon-carbon double bonds separated by at least one carbon atom behave as independent units and can be partly or completely reduced by catalytic hydrogenation or by diimide. cis, trans, /rani-l,5,9-Cyclododecatriene treated with hydrazine and air in the presence of copper sulfate (diimide in situ) gave cij-cyclododecene in 51-76% yield [269]. It appears as if the trans double bonds were reduced preferentially. 

Primary amines can be reduced to their parent compounds by treatment with hydroxylamine-O-sulfonic acid and aqueous sodium hydroxide at 0°. Substituted hydrazines and diimides are believed to be the reaction intermediates in the ultimate replacement of the primary amino group by hydrogen in yields 49-72% [708],... 

Davis and Goddard calculated that the heat of formation (298 K) of singlet H2NN is 90.1 kcal/mol. This value is only 14 kcal/mol below that of molecular nitrogen and two hydrogen atoms, and is 54 kcal/mol above A//f(298 K) for frani-diimide determined experimentally by Willis et al. The relative energies of 1,1- and frani-1,2-diazene have been calculated by several methods these studies have been reviewed by Parsons and Dykstra. It was found using the... 

---