Enyne metathesis methods applied toward the regioselective synthesis of asymmetric cycloalkenes and strained 1,1,3-dienes
Karnofel, William S.
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Ruthenium-catalyzed ring-expanding enyne metathesis provides an efficient approach to cyclodienes. Our group has developed a ring-expansion of cyclopentenes to give cycloheptadienes. The use of complex cyclopentenes led to interesting results; if the ring is strained, it undergoes the enyne metathesis ring-expanding cascade. Proximal steric bulk is believed to be the driving force for regioselective control in ring-expanding enyne metathesis. Lesser steric bulk demonstrates a mixture of regioisomers whereas larger substituents afford one regioisomer. To determine whether these products were a result of low regioselectivity, a simpler cycloalkene was examined. The results suggested lower regioselectivity. Higher regioselectivity can be attained if the α-position contains geminal substitution.