Cycloisomerization of cis-l-Ethynyl-2-Vinyloxiranes

Catalytic cycloisomerization of cis-l-ethynyl-2-vinyloxiranes vas implemented by [Ru(Tp)(PPh3)(CH3CN)2]PF6, which afforded substituted phenols, as shown in 

Stabilized ketene 6S. For l, 2 -disubstituted epoxide, species 6S undergoes 6-endo-dig electrocyclization (path b) [24] to form the six-membered ketone 66, ultimately giving naphthol products. l, 2, 2 -Trisubstituted epoxide species 6S undergoes 5-endo-dig cyclization (path a) to give the ketone species 67, finally producing l-alkylidene-2-indanones. The dialkyl substituent of the epoxide enhances the 5-endo-dig cyclization of species 65 via formation of a stable tertiary carbocation 67. We observed similar behavior for the cyclization of (o-styryl)ethynylbenzenes [15, 16]. Formation of 2,4-cyclohexadien-l-one is explicable according to 6-endo-dig cyclization of a ruthenium-stabilized ketene, vhich ultimately afforded the observed products [25]. 

2-disubstituted epoxides 68a-d bearing a 2-phenyl substituent, their corresponding catalytic cyclizations gave good yields of l-phenyl-2-methyl-lH- indenes 69a-c using the same ruthenium catalyst under similar conditions [25]. It is interesting to note that the same product 69c vas obtained for different epoxides 68c and 68d, bearing a fiuoro substituent at their phenyl C4 and C5, respectively. 

The symmetric character of species 74 provides a rationale for both 4-fluoro 68c and 5-fiuoro 68d substituted epoxides giving the same product (Table 6.2, entries 3-4). 

Catalytic Carbocyclization via Cycloaddition of Ruthenium Vinylidene Intermediates 

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