Methods for the synthesis of phenylacetaldehydes (oxidation, one-carbon chain extension)
were compared by using the synthesis of 4-methoxyphenylacetaldehyde as a model example.
Oxidations of 4-methoxyphenylethanol with activated DMSO (Swern oxidation) or manganese
dioxide gave unsatisfactory results; whereas oxidation with 2-iodoxybenzoic acid (IBX)
produced 4-methoxyphenylacetaldehyde in reasonable (75%) yield. However, Wittig-type
one-carbon chain extension with methoxymethylene-triphenylphosphine followed by hydrolysis
gave an excellent (81% overall) yield of 4-methoxyphenylacetaldehyde from 4-methoxybenzaldehyde
(a cheap starting material). This approach was subsequently used to synthesise a set
of 10 substituted phenylacetaldehydes in good to excellent yields.
Key words
benzaldehyde - phenylacetaldehyde derivatives - homologation reaction