Metal‐Free Catalytic Nucleophilic Substitution of Propargylic Alcohols

Abstract

Organic acids such as PTS efficiently catalyze direct nucleophilic substitutions of the hydroxy groups of propargylic alcohols with a large variety of carbon‐ and heteroatom‐centered nucleophiles. Reactions can be conducted under mild conditions and in air without the need for dried solvents. Reactions on multigram scales are also possible. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Activation of Mononuclear Arene Ruthenium Complexes for Catalytic Propargylation Directly with Propargyl Alcohols

“…Small amounts of 10 (< 15 %) were found as a by-product of the etherification of 1a with EtOH catalyzed by organic acid. [14] A direct access to dipropargyl ethers is interesting, since a,w-diynes are useful building blocks frequently employed for [2 + 2 + 2] cyclization reactions catalyzed by transition metal complexes, [25,26] and also with potential interest as monomers for the preparation of conducting polymers. [27] Propargyl ethers are also key substrates for the ruthenium-assisted retroene reaction and generation of alkene metathesis catalysts.…”

“…[4,5,9] However, for Nishibayashis catalyst very similar diruthenium complexes have been reported to be active also for the propargylic substitution of internal alkynols. [7] On the other hand, catalysts with other metals (Re, [12] Au [13] ) and organic acids, [14] offer their best results with internal alkynols. In our case, experiments with internal alkynols give better results, and support the existence of propargyl cation intermediates instead of allenylidenes, whose formation is restricted to terminal alkynols.…”

“…Several recent reports have showed the rising interest in this propargylation reaction. Rhenium complexes (dppm)ReOCl 3 ), [12] gold salts (NaAuCl 4 ·2 H 2 O), [13] and organic acids (i.e., p-toluenesulfonic acid), [14] have been employed as catalysts with variable results depending on the use of terminal or internal alkynols, and on the particular nucleophiles (alcohols, thiols, heterocyclic and aromatic compounds, etc). Rhenium and gold catalysts are restricted to internal propargyl alcohols and they seem to proceed through stabilized carbonium intermediates.…”

Alcohols in direct carbon-carbon and carbon-heteroatom bond-forming reactions: recent advances

“…Moreover, dilute HCl (10 mol%) also catalysed this reaction in excellent yield. 14 Later, Sanz's group performed a direct alkylation reaction between indoles and tertiary propargylic alcohols catalysed by p-toluenesulfonic acid (PTSA, 5 mol%), in MeCN, at room temperature. 15 Alkylation of furans by benzyl and propargyl alcohols 14,16 in the presence of Brønsted acids as catalyst have attracted the interest of the researchers 17 and selected results are shown in Table 5.…”

“…14 Later, Sanz's group performed a direct alkylation reaction between indoles and tertiary propargylic alcohols catalysed by p-toluenesulfonic acid (PTSA, 5 mol%), in MeCN, at room temperature. 15 Alkylation of furans by benzyl and propargyl alcohols 14,16 in the presence of Brønsted acids as catalyst have attracted the interest of the researchers 17 and selected results are shown in Table 5. Furthermore, the catalytic nucleophilic substitution of tertiary alcohols 11,18,19 using carbon-or heteroatombased nucleophiles in the presence of Brønsted acid has been reviewed 20 and selected results are shown in Table 6.…”