The synthesis and investigation of impurities found in clandestine laboratories: Baeyer-Villiger route part II; synthesis of Phenyl-2- propanone (P2P) analogues from substituted benzaldehydes

We have previously reported phenylpropan-2-one (most commonly known as phenyl-2-propanone, P2P) and methamphetamine derived by-products formed in the Baeyer-Villiger route starting from benzaldehyde. This route is a three step synthesis to P2P; an aldol condensation of benzaldehyde and methyl ethyl ketone (MEK), a Baeyer-Villiger reaction and a subsequent ester hydrolysis. We now report on our investigations into the synthesis of P2P analogues from substituted benzaldehydes via the Baeyer-Villiger route. When strong electron donating substituents are present in the three position of a substituted benzaldehyde (e.g. 3-methoxy and 3,4-methylenedioxy), the resulting aldol reaction is very sensitive to the amount of hydrogen chloride present due to the occurrence of a competing cyclization side reaction yielding various indenes by-products. In contrast, substrates bearing electron-withdrawing substituents react poorly under the Baeyer-Villiger reaction conditions described in this paper. Several new compounds were identified, namely esters 4c, f and g, amongst the known P2P precursors and derivatives. In addition, this work identifies several new by-products in the Baeyer-Villiger route namely 6, 10, 13, 14, 15 and 21; we also report the analytical data for various analogues prepared by this method and this is of value to forensic analysts.