Platinum-Catalyzed Intramolecular Hydroalkoxylation of γ- and δ-Hydroxy Olefins to Form Cyclic Ethers

Abstract

Reaction of 2,2-diphenyl-4-penten-1-ol with a catalytic mixture of [PtCl2(H2C=CH2)]2 (1 mol %) and P(4-C6H4CF3)3 (2 mol %) at 70 degrees C for 24 h led to the isolation of 2-methyl-4,4-diphenyltetrahydrofuran in 78% yield. The platinum-catalyzed hydroalkoxylation of gamma-hydroxy olefins tolerated substitution at the alpha, beta, and gamma-carbon atoms and at the internal and cis and trans terminal olefinic positions. Platinum-catalyzed hydroalkoxylation tolerated a number of functional groups including pivaloate and acetate esters, amides, silyl and benzyl ethers, and pendant hydroxyl and olefinic groups. Pt-catalyzed olefin hydroalkylation was also applicable to the formation of fused- and spirobicyclic ethers and was effective for the hydroalkoxylation of delta-hydroxy olefins to form tetrahydropyran derivatives.

Efficient Intramolecular Hydroalkoxylation of Unactivated Alkenols Mediated by Recyclable Lanthanide Triflate Ionic Liquids: Scope and Mechanism

“…The present activation parameters-enthalpy (DH°) = 18.2 (9) kcal mol tractions, efficient transformations remain elusive due factors such as the large OÀH bond enthalpies, the modest reactivity of electron-rich olefins with nucleophiles, high catalyst costs, and catalyst metal toxicity. [5,6] There has been a growing research effort to address the aforementioned issues and to develop more efficient and selective hydroalkoxylation catalysts for this attractive transformation. [4][5][6][7] For intramolecular alkenol HO/cyclizations, two possible products, exemplified by the exo and endo ethers shown in Equation (1), are a priori possible where either exo-trig or endo-trig cyclization to five-or six-membered rings is allowed by the Baldwin ring-closure rules.…”

“…[5,6] There has been a growing research effort to address the aforementioned issues and to develop more efficient and selective hydroalkoxylation catalysts for this attractive transformation. [4][5][6][7] For intramolecular alkenol HO/cyclizations, two possible products, exemplified by the exo and endo ethers shown in Equation (1), are a priori possible where either exo-trig or endo-trig cyclization to five-or six-membered rings is allowed by the Baldwin ring-closure rules. [9] Although direct catalytic intramolecular OH addition to alkenes is attractive, such seemingly simple processes have not generally proven efficient and frequently lack generality.…”

“…[2] Currently, oxygen heterocycles are catalytically accessible by either direct Wacker oxidative cyclization [3] or by means of intramolecular hydroalkoxylation (HO), [4][5][6][7] with the latter being a relatively unexplored transformation mediated by a limited number of catalysts. In principle, intramolecular hydroalkoxylation is a concise, elegant route that should be possible to effect with 100 % atom efficiency and with negligible waste coproduction.…”

Electrophilic Activation of Alkenes by Platinum(II): So Much More Than a Slow Version of Palladium(II)

“…(20)]. [83] The system is generally selective for oxygen addition to the more highly substituted carbon atom, and five-or six-membered rings may be formed. The selectivity for hydroalkoxylation (oxyplatination followed by Pt À C protonolysis) in the platinum system contrasts markedly with palladium-based systems, which tend to give oxidized products through a Wacker-type oxypalladation/b-hydride elimination mechanism.…”

Efficient Gold‐Catalyzed Hydroamination of 1,3‐Dienes

“…This method can be extended to the hydroamination of simple alkenes (Scheme 1). [4] These types of transformations have also been carried out with palladium, [5] platinum, [6] ruthenium, [7] and Brønsted acids. [8,9] However, they are limited in scope, and in the case of palladium, b-hydride elimination occurs to afford unsaturated products.…”