ABSTRACT
This chapter draws on three categories – removal of oxygen, addition of hydrogen and the gain of electrons. Reduction of the alkyne is required to occur in a manner that gives the trans-alkene. In general, homogeneous hydrogenation catalysts favour the formation of trans-alkenes. Reduction of the enone with sodium in ethanol, an electron-transfer oxidant, affords the trans-2,3-dimethylcyclohexan-1-one. The aldehyde is more reactive than the ketone and can be selectively protected as a cyclic acetal by reaction with one mole of ethyleneglycol. Reduction with lithium aluminium hydride, addition of a controlled amount of water to hydrolyse the aluminium alkoxy complex followed by deprotection complete the sequence. Reduction with aluminium, in the presence of nickel chloride in tetrahydrofuran, gives the dialdehyde, along with some of the corresponding diol. The use of diimide in reducing alkenes is limited since reduction of sterically hindered alkenes is slower than disproportionation of diimide to nitrogen and hydrazine.
