Syntheses and some reactions of aliphatic 1,2,3‐trienes

Trienes of the type R(R′)CCCCH 2 (R and R′ are H or alkyl) have been prepared in good to excellent yields from 1,4‐dichloro‐2‐alkynes, R(R′)C(Cl)CCCH 2 Cl, and zinc dust or sodium iodide in dimethyl sulfoxide. The dichloro compounds were obtained from the corresponding 1,4‐dihydroxy‐2‐alkynes and thionyl chloride. The 1,4‐diols were synthesized from propargyl alcohol; the adduct of this alcohol and 2,3‐dihydropyran, , was coupled with an aldehyde RCHO or a ketone RR′CO (R and R′ are alkyl) under Grignard conditions. The resulting products R(R′)C(OH)CCCH 2 OT.H.P. (T.H.P. = tetrahydropyranyl) were treated with a catalytic amount of p ‐toluenesulfonic acid in an excess of methanol, furnishing the diols R(R′)C(OH)CCCH 2 OH (R = H and R′ = alkyl or R and R′ are both alkyl) in good overall yields. Reaction of the cumulenes with equivalent amounts of alkali amide in liquid ammonia followed by hydrolysis of the reaction mixtures afforded the isomeric 3,1‐enynes, R(R′)CCHCCH, in good yields. Buta‐1,2,3‐triene, CH 2 CCCH 2 , and hexa‐1,2,3‐triene, CH 3 CH 2 CHCCCH 2 , were isomerized by sodium methoxide in liquid ammonia to the enynes vinylacetylene, HCCCHCH 2 , and hex‐2‐en‐4‐yne, CH 3 CHCHCCCH 3 , respectively. In the case of buta‐1,2,3‐triene also a considerable quantity of the 1,4‐adduct of methanol, 1‐methoxy‐2‐butyne, CH 3 CCCH 2 OCH 3 , was isolated. The addition of ethanethiol to buta‐1,2,3‐triene and hexa‐1,2,3‐triene proceeded readily, yielding mixtures of isomeric adducts, C 2 H 5 SCH 2 CHCCH 2 and C 2 H 5 SCH 2 CCCH 3 , in the first case, and C 2 H 5 CH(SC 2 H 5 )CHCCH 2 , C 2 H 5 CH(SC 2 H 5 )CCCH 3 and C 2 H 5 SCH 2 CHCCHC 2 H 5 , in the second case. These compounds lost ethanethiol when treated with alkali amide in liquid ammonia, the 3,1‐enynes, HCCCHCH 2 and HCCCHCHC 2 H 5 , respectively, being produced.