We have investigated u,a-dichloroketimines 2 in connection with comprehensive research 3 on the reactivity of halogens in the a-position to a sp 2 -hybridised carbon atom. The starting materials were prepared by the condensation of a methyl ketone with an aniline in benzene with para-toluenesulphonic acid as catalyst, followed by chlorination with two equivalents of N-chlorosuccinimide (O'C, CC14) which gave N-2-(l,l-dichloroalkylidene)anilines 2 in excellent yields 435 C6H6 JCJ 0 R' do 0 R' RJ' N QNH2&m-RL2-y e R,&c, 1 2 Cl Peactions of N-2-(l,l-dichloroalkylidene)anilines 2 with nucleophilic reagents -(e.g. NaOCH3/CH30H, under reflux) led to both nucleophilic substitution and to Favorskii-type rearrangement. Nucleophilic substitution provided N-2-(l,l-dimethoxyalkylidenejanilines 3, which were easily hydsolysed to the difficultly accessible l,l-dimethoxy-2-alkanones. The new analogue of the Favorskii-rearrangement afforded exclusively cis N-aryl u,5-unsaturated imidates 2 (imino estersj6, which are thermo-labile and isomerize rapidly to the corresponding trans derivatives7.
As is shown in the table, the ratio dimethoxyketimine >/imidate 2 is depending on the R-group and on the medium. Substitution increases with increasing length of the R-group. A very slow reaction was found for 2c (R=LBu) and no -Favorskii-like rearrangement occured. The amounts of imidate 4 decreased when sodium ethoxide is used instead of sodium methoxide.
No reaction was found with KOtBu/tBuOH. On the other hand when the reaction was executed with sodium methyl--ate in less polar medium (Et20 or LPr20) primary 8 N-2-(l,l-dichloroalkylidene)-