Addition reactions Alkynes Dienes Ketones

Abstract In the present chapter we discuss transition-metal-catalyzed phosphorus-hydrogen (P-H) bond addition to the triple bond of alkynes and to the double bond of alkenes, dienes, imines, aldehydes and ketones. Main attention is paid to highlight the factors responsible for development of highly efficient catalytic systems and to carry out the addition reaction with high stereo-, regio- and enantioselectivity. 

Terminal allenes.1 A synthesis of 1,2-dienes (3) from an aldehyde or a ketone involves addition of ethynylmagnesium bromide followed by reaction of the adduct with methyl chloroformate. The product, a 3-methoxycarbonyloxy-l-alkyne (2), can be reduced to an allene by transfer hydrogenolysis with ammonium formate catalyzed by a zero-valent palladium complex of 1 and a trialkylphosphine. The choice of solvent is also important. Best results are obtained with THF at 20-30° or with DMF at 70°. 

Hydrocyanation is the formal addition of hydrogen cyanide to alkenes. alkynes, and dienes to yield nitriles. These reactions can be catalyzed by various copper, cobalt, nickel and palladium catalysts modified with phosphanes and phosphites and/or Lewis acids. Hydrocyanation of carbonyl groups in aldehydes and ketones is covered in Section D.l.3.7. 

In 2002, Rawal developed a tandem reaction via multifunction palladium catalysis combining haloallylation and the Wacker-Tsuji oxidation.53 For example, internal alkyne 68 first underwent a bromoallylation to give a 1,4-diene, which was subsequently oxidized to the methyl ketone 69 without addition of the palladium catalyst. 

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