Halogenated acetals prepn. - by cationic halogenation of unsaturated esters and treatment with an alcohol

摘要

The acetals of halo ethylenic aldehydes of formula (I) are prepd. from an ester (II) by treatment with a cationic halogen (Cl+, Br+, or I+), followed by prim. or sec. alcohol or a glycol. (where R1 - R5 = H, 1-6C alkenyl, or o-6C alkenyl, not having the double bond in position 1-2; n = 0-4; R6 = 1-6C alkyl or the tow groups R6 = R'6-where R'6 = 2-6C alkylene, opt. substd. by OH or alkoxy of 1-4C; X = Cl, Br or I R = 1-6C alkyl). Cpds. are intermediates for organic synethses., esp. for preparation of retinal (Vit A aldehyde). A typical compound (I) is 1,1-dimethoxy-3-methyl-4-chloro-2-butene b.pt. 38-38.5 degrees C. This was prepd. from 1-acetoxy-3-methyl-1,3-butadiene by treatment with t. butyl hypochlorite followed by methanol.