Hydrogen transfer from diimide

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. 

In agreement with this mechanism is the fact that the stereochemistry of addition is syn.44 The rate of reaction with diimide is influenced by torsional and angle strain in the alkene. More strained double bonds react at accelerated rates.45 For example, the more strained trans double bond is selectively reduced in Z,K-1,5-cyclodecadiene. 

Diimide selectively reduces terminal over internal double bonds in polyunsaturated 

Addition of Hydrogen at Carbon-Carbon Multiple Bonds 

Reduction of Carbon-Carbon Multiple Bonds, Carbonyl Groups, and Other Functional Groups 

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The reduction of 1,5-dimethylcyclopentene (29a) and 1,6-dimethylcyclohexene (29b) results in the preferential formation of the trani-dimethyl products (31 equation 12). In these cases the approach of the diimide occurs from the direction which will allow the methyl groups to move away from each other, i.e. in the transition state for hydrogen transfer from diimide the direction of the approach of diimide is dictated by torsional effects generated between the methyl groups. ... 

Formally, the bishomo-Diels-Alder reactions of bi(cyclopropyl) derivatives or [(2a+2a) + 2n] additions could also be viewed as group-transfer reactions, since two cyclopropyl carbon atoms are transferred to a Ti-bond (all-carbon analog, e.g. of hydrogen transfer from a diimide to a Tt-bond). 

The ultimate fate of diimide is sealed by its capacity to function both as a hydrogen acceptor and a powerful hydrogen donor. This latter property allows for the concerted, pericyclic hydrogen transfer from the c -diimide isomer, a less stable isomer in solution, as presented in Scheme 16.12. 

The other well-known type of group transfer reaction is represented by the concerted syn delivery of two hydrogen atoms from the reactive intermediate diimide 1.25 to an alkene or alkyne, driven by the formation of the stable molecule nitrogen. 

Stereochemical studies on the reduction of C==C and by diimide have shown that the transfer of hydrogens from diimide occurs in a completely syn manner. The reduction of (4) and (5) with dideute-riodiimide, generated by the deuterolysis of dipotassium azodiformate, resulted in the formation of the meso- and ( )-reduction products (6) and (7) in at least 97% stereospecificity (the lower limit of detectability with IR spectral analysis). The reduction of diphenylacetylene (8) produces only c/ s-stilbene (9) as an intermediate reduction product. It was considered that the reduction of multiple bonds by diimide occurred as a synchronous transport of a pair of hydrogens to a single face of the rr-system via a transition state represented as (10). ... 

In a double hydrogen atom transfer between d.v-9,10-dihydronaphthalcnc 6.120 and 1,2-dimethylcyclohex-ene 6.121, analogous to the diimide reduction 6.16, the two hydrogens leave from the same surface of the dihydronaphthalene, and arrive on the same surface of the cyclohexene to give the r .v-dimcthylcyclohcxanc... 

Another type of group transfer reaction is the transfer of hydrogens from diimide to an alkene or alkyne. 

During diimide reductions considerable nitrogen gas is formed by the disproportionation of diimide. Theoretical calculations on the energy surfaces for the transfer of hydrogen from c s-diimide to cis- and... 

The transfer of one or more groups from one molecule to another in a concerted process is known as group transfer reaction. In most of the cases hydrogen is transferred. Only a few reactions of this class are known. Among them, the most common are ene reactions and diimide reduction. 

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