Transformation of Propargyl Alcohols

We have already revealed the unique coupling reactions of two moles of propargyl alcohols on the Ru /Ru complex 6, which give two types of diruthenacycle complexes depending upon the substituents of the alcohols. Formation of the terminal allenylidene complexes [Cp RuCl(/i-SPr )2Ru(=C=C=CR2)Cp ](OTf) from the cationic diruthenium complex 4 and propargyl alcohols has also been 

---

This chapter is mainly a summary of our recent findrngs on the thiolate-bridged drruthenium complex-catalyzed novel organic transformation of propargylic alcohols. 

The ability of the binuclear complex [Cp RuCl(p2-SR)2RuCl(Cp )] to generate cationic allenylidene complexes by activation of terminal prop-2-ynols in the presence of NH4BF4 as a chloride abstractor opens the way to a variety of catalytic transformations of propargylic alcohols involving nucleophilic addition at the Cy atom of the ruthenium allenylidene intermediate (Scheme 19). This leads to the formation of a functional ruthenium vinylidene species which tau-tomerizes into an -coordinated alkyne that is removed from the ruthenium centre in the presence of the substrate. 

Carbonylation and hydroformylation. With PEG as a PTC, COjCCO), mediates the carbonylation of benzylic halides. A more complex system is used in the transformation of propargylic alcohols into 2-alkylidenesuccinic acids (9 examples, 84-97%). Very similar results are obtained from the carbonylation of alkynyl ketones. "... 

This study demonstrates that the addition of the 2-diazopropane with the triple bond of propargyl alcohols is regioselective, and affords new antibacterial 3H-pyrazoles. The photochemical reaction of these 3H-pyrazoles selectively leads to a- and 6-hydroxy cyclopropenes. The overall transformation constitutes a simple straightforward route to substituted cyclopropenyl alcohols without initial protection of the propargyl alcohol hydroxyl group. 

Recently, Lewis-acid-catalyzed nucleophilic substitution reactions of propargyl alcohols have been described. In general, costly transition metals such as Ru, Re, Pd or Au are used in these transformations. At this point Bi(III) salts are believed to be a cheap and environmentally benign alternative. 

In parallel, since the first preparation of allenylidene-metal complexes in 1976, the formation of these carbon-rich complexes developed rapidly after the discovery, in 1982, that allenylidene-metal intermediates could be easily formed directly from terminal propargylic alcohols via vinylidene-metal intermediates. This decisive step has led to regioselective catalytic transformations of propargylic derivatives via carbon(l)-atom bond formation or alternately to propargylation. Due to their rearrangement into indenylidene complexes, metal-allenylidene complexes were also found to be catalyst precursors for olefin and enyne metathesis. 

The double phosphinylation of propargylic alcohols with diphenylphos-phine oxide to form 2,3-bis(diphenylphosphinyl)-1-propenes is catalyzed by a thiolate-bridged diruthenium complex (Scheme 28) [69]. It has been shown that the reaction proceeds via three ruthenium-catalyzed transformations propargylation of the phosphine oxide, alkyne to allene isomerization, and addition of phosphine oxide to the allene structure. 

The best catalyst to perform this reaction is the stable binuclear [Ru(02CH)(C0)2-(PPh3)]2 complex, which makes possible the transformation of bulky alcohols such as steroid derivatives with retention of configuration at the propargylic carbon atom [57], and the preparation of y3-oxopropyl esters from propargylic alcohols as well as y-oxobutyl esters from butynol (Scheme 8.16) [56]. 

The transient zirconocene butene complex, 105, has proved to be useful in a number of organic transformations. For example, butene substitution of zirconocene alkene complexes with alkoxy-substituted olefins results in /3-alkoxide elimination to furnish the zirconocene alkoxy compounds (R = Me, 123 R = Bnz, 124) (Scheme 16).50,51 Addition of propargyl alcohols to the zirconocene butene complex, 105, affords homoallylic alcohols. These reactions are of limited utility owing to the lack of stereoselectivity or formation of multiple products. Positioning the alkoxide functional group further down the hydrocarbyl chain allows synthesis of cyclopropanes, though mixtures of the carbocycle and alkene products are obtained in some cases (Scheme 16).52... 

Beyond simple coordination, metal catalysts may transform unsaturated substrates to enable C-P bond formation. For example, Ru-catalyzed hydrophosphination of propargyl alcohols was proposed to proceed via nucleophilic attack of diphenylphosphine on the Ru=C group in a vinylidene complex (Scheme 35) [57]. 

Microbial transformations also occupy a very important position in the synthesis of enantiomerically pure compounds. Mori and Akao utilized the selective hydrolysis of the acetate derivatives of propargylic alcohols with Bacillus subtilis. However, the optical purities of the products were only up to 74% (Scheme 21.23). 

The transformation of propargyl vinyl ethers into 2f/-pyrans is also possible with electrophilic iodine or bromine as demonstrated recendy by Xin and co-workers (Scheme 22) (15TL401). Firstly, propargylic alcohols 65 and bis-acceptor-substituted alkynes 66 are converted in situ into propargyl vinyl ethers.While no transition metal-catalysts are involved, the cychzation is induced by the initial formation of a halonium ion. The halonium ion is then attacked by the internal vinyl group and, after deprotonation, the product 67 is formed. The halogenated 2H-pyrans 67 were obtained in good yields under mild conditions. 

A single case of thiophene synthesis by gold-catalyzed dehydrative cyclization of a thiolated propargyl alcohol has been reported. Compared with the corresponding transformation of propargyl diols or aminoalcohols (Sections 4.1 and... 

---