Boron Trichloride → 4-Chloro-3,5-dimethyl-2-(prop-2-en-1-yl)phenol

Participants

Reaction Steps

These o-allyl phenols are accessible in a simple and conventional manner by the Claissen transposition from the corresponding phenol allyl ethers at elevated temperature or in the cold in the presence of boron trichloride, it being necessary, of course, to take into account the different reactivities of the various phenols (cf. Houben-Weyl, Phenole I). For example, the transposition of phenol allyl ether requires 200° C. for about 10 hours, giving an approximately quantitative yield. On the other hand, 4-chloro-3,5-xylenol allyl ether reacts completely within 2 hours, and the 2-allyl-4-chloro-3,5-xylenol (MP 65° C.) can be isolated in an approximately quantitative yield only when the heat treatment is immediately stopped thereafter, on account of the threat of isomerization to the corresponding benzodihydrofuran (MP 36° C.). On the other hand, 2,4,5-trichlorophenol allyl ether is transposed above 150° C. in a very violent and highly exothermic reaction; this is mentioned especially for safety reasons.

Provenance & Evidence