PREPARATION AND CHEMICAL BEHAVIOR OF 2,3-DIETHYNYL-1,3-BUTADIENE

The two 2,3-diethynyl-1,3-butadiene derivatives 1b and 1c were prepare d from 2,3-dichloro-1,3-butadiene (26) and the Grignard reagents 19b a nd 19c by Kumada coupling. Desilylation of 1b provided the parent mole cule la. The title compounds were used for the preparation of numerous new enediyne systems by [2 + 4] cycloaddition. The dienophiles employ ed include maleic anhydride (27a), diethyl fumarate (29), tetracyanoet hylene (31), diethyl azodicarboxylate (33), and dimethyl acetylenedica rboxylate (35). With p-quinones such as p-benzoquinone (44) as dienoph iles the expected mono- and bisadducts are formed which were dehydroge nated to the bis- and tetrakis(trimethylsilylethynyl)naphtho- and -ant hraquinones 47 and 48, respectively, by treatment with DDQ. Heating of Ib in THF at 65 degrees C caused dimerization to the 1,5-cyclooctadie ne derivative 56, which was desilylated to 1,2,5,6-tetraethynyl-1,5-cy clooctadiene (59) by treatment with potassium fluoride in DMF. 1b is a pproximately 15 times less reactive than 2,3-dimethyl-1,3-butadiene (5 4) towards maleic anhydride (27a).