A new modification of the pomeranz–fritsch isoquinoline synthesis

Schiff's bases formed from a variety of alkoxybenzaldehydes and aminoacetaldehyde dimethyl acetal have been hydrogenated to the corresponding benzylamines and converted into N-tosylates. The latter are readily cyclised in dilute mineral acid to isoquinolines in a one-pot reaction; intermediates in this reaction are N-tosyl-1,2-dihydroisoquinolines which can be isolated. N-Benzyl-N-tosylaminoacetaldehyde dimethyl acetal on treatment with dilute acid under the same conditions as for the cyclisation reactions gave N-benzyl-N-tosylaminoacetaldehyde, and then N-tosylbenzylamine; other substituted benzylamino-acetal derivatives similarly when the benzyl group lacked sufficiently activating substituents for cyclisation of the acetal.