Allenyne Alcohols

Caution-. Use rubber gloves during the work-up, the allenyne alcohol probably is a skin irritant. 

Both 1,1- and 1,2-disubstituted allenes participate well. If both substituents bear allylic hydrogen, the issue becomes regioselectivity of (3-hydrogen elimination. An obvious solution is to activate one of the possible (3-Hs by proper choice of the substituent. A carbonyl group serves that role, as illustrated in Equations 1.65 and 1.66 [58]. In these cases, the tris-acetonitrile precatalyst was employed, which does not require the addition of an alkyne as a cocatalyst. Interestingly, competing the reaction of a propargyl alcohol with that of an allene as in the case of allenyne 58 (Equation 1.67) showed complete chemoselectivity for reaction of the allene. 

When 1,6-allenynes were reacted with nucleophiles such as alcohols in the presence of Cp RuCl(cod) in methanol or in the presence of [Cp Ru(CH3CN)3] PFs in THF, functionalized 1,2-bisalkylidenecyclopentanes were produced via stereoselective addition of nucleophiles to ruthenacyclopentenes [107] [Eq. (46)]. This ruthenacycle obtained by oxidative coupling of the triple bond and the terminal double bond captures a proton from alcohol at the y-position of the metal affording a mono-carbene intermediate able to undergo a nucleophilic attack of alcohol. 

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