Trisubstituted alkenes of E geometry have been prepared by anti additi
on of Grignard reagents to 1,4-difunctionalized but-2-ynes. Addition o
f primary, secondary and aromatic Grignard reagents to but-2-yne-1,4-d
iol provided (E)-2-substituted but-2-ene-1,4-diols as major products a
long with the corresponding 2-substituted buta-2,3-dien-1-ols. Additio
n of phenylmagnesium bromide to the mono- and di-methyl ethers of but-
2-yne-1,4-diol gave 2,3-diphenyl-1,3-diene. Treatment of 4-dimethylami
nobut-2-yn-1-ol with primary alkyl and alkenyl Grignard reagents affor
ded the 2-substituted anti addition product regiospecifically, stereos
pecifically and in high yield. Reaction of 1-dimethylamino-4-methoxybu
t-2-yne with butylmagnesium bromide provided only the 3-substituted an
ti addition product in good yield.