INTRAMOLECULAR ALKYLATION OF AROMATIC-COM POUNDS .32. A REGIOSELECTIVE SYNTHESIS OF 4-METHYL-1-PYRINDAN-5-ONE

The enamine 7 reacts with crotonic aldehyde in the presence of p-tolue nesulphonic acid via the intermediate 8 to yield regioselectively the unknown title compound 9. In alkaline medium, 9 is also formed from 7 and acetylacetaldehyde dimethyl acetal as well as small amounts of 11 and 12; under acidic conditions, however, mixtures of the regioisomers 9/9a are obtained in poor yield. 9a can be separated by fractional cr ystallisation of the hydrochlorides. Corresponding to 7 the homologous enamine 13 and acetylacetaldehyde acetal by alkaline catalysis gives the 4-methyltetrahydroquinolinone 1, respectively. Improved experiment al details for an efficient preparation of the starting compounds 3 an d 4 are given.