Reactions of Ruthenium Cp Phosphine Complex with 4,4-Disubstituted-1,6-Enynes: Effect of Methyl Substituents in the Olefinic Fraction

We studied chemical reactions of Cp(PPh3)2RuCl with nine 1,6-enyne compounds (1−4, 8, 12, 19, 21, and 22) in which the triple bond is associated with propargylic alcohol and the olefinic group has various substituted methyl groups. For the enyne compounds 1−3 with no substituted methyl group, the reaction takes place at the propargylic alcohol first giving the allenylidene complex 6 which could undergo a skeletal rearrangement to yield the disubstituted vinylidene complex 7. By changing the propargylic alcohol to propargylic ether, the reaction gives the carbene complex 10 as the major product and the butadiene complex 9 by a cyclization reaction as the minor product. For enyne 12 with two methyl groups at the terminal carbon of the olefinic part, formation of either of the carbene complexes 15 and 16 with a substituted cyclopentenyl ring at Cα or the vinylidene complex 17 is controlled by the use of solvent. For the formation of 15 and 16, a C−C bond-forming cyclization reaction is proposed to occur at C...