Page 415 - Advanced Organic Chemistry Part B - Reactions & Synthesis

388 is most successful is Lindlar’s catalyst, a lead-modified palladium-CaCO catalyst. 41
3
A nickel-boride catalyst prepared by reduction of nickel salts with sodium hydride is
CHAPTER 5 42 43
also useful. Rhodium catalysts have also been reported to show good selectivity.
Reduction of
Carbon-Carbon Multiple
Bonds, Carbonyl
Groups, and Other 5.1.5. Hydrogen Transfer from Diimide
Functional Groups
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.

C C
HN NH + C C H H C C
H H
N N N N
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,E-1,5-cyclodecadiene.

NH NH 2
2
Cu 2+, O 2 Ref. 46

Diimide selectively reduces terminal over internal double bonds in polyunsaturated
systems. 47
Reduction by diimide can be advantageous when compounds contain functional
groups that would be reduced by other methods or when they are unstable to hydro-
genation 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 decar-
boxylation of azodicarboxylic acid. Entry 2, which illustrates another convenient
method, thermal decomposition of p-toluenesulfonylhydrazide, is interesting in that it

41 H. Lindlar and R. Dubuis, Org. Synth., V, 880 (1973).
42
H. C. Brown and C. A. Brown, J. Am. Chem. Soc., 85, 1005 (1963); E. J. Corey, K. Achiwa, and
J. A. Katzenellenbogen, J. Am. Chem. Soc., 91, 4318 (1969).
43 R. R. Schrock and J. A. Osborn, J. Am. Chem. Soc., 98, 2143 (1976); J. M. Tour, S. L. Pendalwar,
C. M. Kafka, and J. P. Cooper, J. Org. Chem., 57, 4786 (1992).
44
E. J. Corey, D. J. Pasto, and W. L. Mock, J. Am. Chem. Soc., 83, 2957 (1961).
45
E. W. Garbisch, Jr., S. M. Schildcrout, D. B. Patterson, and C. M. Sprecher, J. Am. Chem. Soc., 87,
2932 (1965).
46 J. G. Traynham, G. R. Franzen, G. A. Kresel, and D. J. Northington, Jr., J. Org. Chem., 32, 3285 (1967).
47
E. J. Corey, H. Yamamoto, D. K. Herron, and K. Achiwa, J. Am. Chem. Soc., 92, 6635 (1970);
E. J. Corey and H. Yamamoto, J. Am. Chem. Soc., 92, 6636, 6637 (1970).