Enyne with sulfonamides

Quite recently, the alkenylative cyclization of enynes with ethylene was achieved using Cp RuCl(cod) as a precatalyst at room temperature [92]. This mild and selective transformation was applied to a sulfonamide 95 to produce the corresponding pyrrolidine derivative 96 (Eq. 37). A ruthenacyclopentene intermediate was proposed for this novel cyclization. 

Complexation of propargyl aldehydes to cobalt also enhances the reactivity and enantioselectivity of the addition of alkylzinc reagents. This fact was used to create non-racemic enyne-ol 88 reacting the aldehyde 86 with bis-homoallylzinc in the presence of a chiral frzs-(sulfonamide) and Ti(OlPr)4. The resulting complexed substrate 87 underwent the PKR promoted by TMANO in a one pot fashion (Scheme 25) [122]. 

Endo-skeletal rearrangements also take place with 1,6-enynes, bnt the proposed mechanism is just a variation of the exo-single-cleavage rearrangement. Formed by endo cyclization, bicyclo[4.1.0]hept-4-ene derivatives arise in some cyclizations of 1,6-enynes by proton loss and protodemetalation ofthe endo cyclopropylcarbene. " That is the case from 1,6-enynes tethered as sulfonamides and in the intramolecular cyclization of 1,6-enol ethers with alkynes (equation 40). ... 

Intramolecular additions of alcohols or amines to olefins are recognized as useful methods to provide heterocyclic compounds. Kozmin and Zhang have achieved a gold-catalyzed synthesis of heterobicyclic alkenes by double cyclization of alcohols or sulfonamides which have a 1,5-enyne moiety [175]. As a typical example, unsaturated alcohol (95) is smoothly converted to 6-oxabicyclo[3.2.1]octane (96) in 90% yield using a 5 mol% of AuCls catalyst (Scheme 18.34). Cyclic ethers are also available from homopropargylic ethers with pendant alcohols through gold-catalyzed... 

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