ETHYNYLSILANES .4. EFFECT OF TEMPERATURE ON DIELS-ALDER ADDITION OF ACETYLENIC DIENOPHILES TO 1-TRIMETHYLSILYLCYCLOPENTADIENE

Dimethyl acetylenedicarboxylate was treated with 1-trimethylsilylcyclopentadiene to yield a mixture of 7-trimethylsilyl- and 5-trimethylsilyl-2,3-bis(methylcarboxylato)bicyclo[2.2.1]heptadienes. Thermal isomerization of the 7-trimethylsilyl derivative to the 5-trimethylsilyl isomer was shown not to occur. Reactions between (CH3)3SiC蠁CR, where R is H, COCH3, or CO2C2H5, and 1-trimethylsilylcyclopentadiene were carried out at 180-260°, and only vinyl-substituted derivatives were obtained. It is suggested that 1-trimethylsilylcyclopentadiene undergoes temperature-dependent tautomerism, which may be viewed as a 1,3-proton shift, to form 3-trimethylsilylcyclopentadiene. The reactions between the various dienophiles and this tautomeric form of the diene would be expected to yield the products observed at the high temperature. © 1968, American Chemical Society. All rights reserved.