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Commercial ferrocenium hexafluorophosphate ([FeCp 2 ]PF 6 ) and ferrocenium boronic acid hexafluoroantimonate ([FcB(OH) 2 ]SbF 6 ) were found to be efficient catalysts for the etherification of terminal, tertiary, cyclopropyl-substituted propargylic alcohols through nucleophilic substitution with primary and secondary alcohols. The alcohol nucleophiles and the propargylic alcohols were employed in a nearly equimolar amount and no further additives were required. After 2 h reaction time at 40°C in CH 2 Cl 2 and 3 to 5 mol-% catalyst load, aromatic, cyclopropyl-substituted propargylic alcohols gave rearranged, conjugated ene-yne products as single isomers in 35 to 73 % isolated yields. Cyclopropyl-substituted propargylic alcohols [a] 7349 Accordingly, we decided to synthesize cyclopropyl-substituted propargylic alcohol substrates (4 in Scheme 1c) to investigate whether the reaction proceeds through a radical mechanism. Cyclopropyl-substituted radicals 6 (Scheme 1c) may ringopen to form alkenes, but carbocation 5 may also have this tendency (vide infra). As exemplified in Scheme 1c, ene-ynes 7 can form through rearrangement if a cyclopropyl-substituted propargylic alcohol 4 is employed. [35] The employment of cyclopropyl-substituted propargylic alcohols in reactions with alcohols to give conjugated, achiral enynes has been reported previously only four times, utilizing Yb(OTf ) 3 , [36a] triflic acid (TfOH), [36b] HAuCl 4[36c] and ruthenium complexes [36d] as catalysts. In these reports, the nucleophile was either the solvent [36b,36c] or employed in large excess. [36a,36d] Herein, we report ferrocenium-catalyzed substitution reactions with these substrates and isolated both ene-yne products and cyclopropylsubstituted products, depending on the substituent R in 4. Experimental evidence points toward an ionic mechanism through carbocation 5 (Scheme 1c). [37] Eur.Scheme 2. Formation of the cyclopropyl-substituted intermediate 21 and ring-opening.

New chiral ruthenium(II) allenylidene complexes were synthesized, and their reactivity with nucleophiles to give alkynyl complexes was investigated. The new allenylidene complex (R Ru ,R ax )-[Ru(Ind)(PPh 3 )(6){C CC(t-Bu)(2-naphthyl)}] + PF 6 − was synthesized from the chloro precursor complex (R Ru ,R ax )-[RuCl(Ind)(PPh 3 )( 6)] and the racemic propargylic alcohol HCCC(OH)(t-Bu)(2naphthyl) and obtained in 96% yield, where (R ax )-6 is a chiral phosphoramidite and Ind an anionic indenyl ligand. The precursor and the allenylidene complex are chiral-at-metal, and the chiral information is completely transferred from the chloro precursor to the product allenylidene complex, both of which show the same absolute configuration, as demonstrated by X-ray diffraction. Together with the known allenylidene complex (R Ru ,R ax )-[Ru(Ind)(PPh 3 )(6)(CCCPh 2 )] + PF 6 − , the attack of n-BuLi, MeLi, LiCCPh, and lithium 1-phenylethenolate nucleophiles on the allenylidene chain of (R Ru ,R ax )-[Ru(Ind)(PPh 3 )-( 6){CCC(t-Bu)(2-naphthyl)}] + PF 6 − was investigated. The nucleophiles (Nu) reacted selectively with the gamma carbon of the allenylidene complexes to give the alkynyl complexes (R Ru ,R ax )-[Ru(Ind)(PPh 3 )(6)(CC−CPh 2 Nu)] and (R Ru ,R ax )-[Ru(Ind)(PPh 3 )(6){CC−C(t-Bu)(2-naphthyl)Nu}] in 40% to 96% isolated yields. In the case of (R Ru ,R ax )-[Ru(Ind)(PPh 3 )-(6){CC−C*(t-Bu)(2-naphthyl)Nu}], the gamma carbon C* becomes stereogenic upon attack of the nucleophiles. As assessed by 31 P{ 1 H} NMR, diastereodifferentiation took place, and the alkynyl complexes were isolated as diastereomeric mixtures with diastereomeric ratios between 60:40 and 84:16. The diastereodifferentiation originated only from the stereogenic metal center and the monodentate, chiral ligand. The study allows for investigation of stereoselective, nucleophilic attack of allenylidene complexes to give optically active, quaternary alkynes, which play a role in potential catalytic versions of nucleophilic substitution reactions of propargylic alcohols.

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