Intramolecular Rotations in 2,2-Dimesityl-1-(9-anthryl)- and -1-(9-triptycyl)vinyl Acetates

Article abstract of DOI:10.1021/jo00086a015

2,2-Dimesityl-1-(9-anthryl)vinyl acetate (3) and 2,2-dimesityl-1-(9-triptycyl)vinyl acetate (4) were prepared.The rotation of the mesityl and 9-anthryl rings in 3 and of the mesityl rings and triptycyl substituent in 4 around their bonds to the vinylic carbon were investigated by DNMR.For each system an identical rotational barrier was measured for each substituent, indicating a correlated rotation.The rotational barriers were 16.7 +/- 0.1 kcal mol^-1 for 3 and 17.0 +/- 0.1 kcal mol^-1 for 4.The suggested rotational mechanism is a three-ring flip for 3 and a correlated (geared) rotation for the three rotors of 4.The latter process involves a two-ring flip of the two mesityl rings and a rocking process of the triptycyl moiety in which only one of its rings eclipses the C=C plane in the transition state.