Efficient Intramolecular Hydroalkoxylation/Cyclization of Unactivated Alkenols Mediated by Lanthanide Triflate Ionic Liquids

Dzudza, Alma; Marks, Tobin J.

doi:10.1021/ol8029559

Cited by 89 publications

(36 citation statements)

References 50 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In a recent a communication, we briefly reported for a limited set of substrates, that in imidazolium-based ILs, [LnA C H T U N G T R E N N U N G (OTf) 3 ]-mediated alkenol HO/cyclizations are efficient processes for cyclic ether synthesis with Markovnikov selectivity. [31] Herein we present a detailed report on the broad Scheme 2. Common ionic liquid cations and anions.…”

Section: A C H T U N G T R E N N U N G [Alkenol]mentioning

confidence: 99%

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

Dzudza

Marks

2010

Chemistry A European J

Self Cite

View full text Add to dashboard Cite

Lanthanide triflate complexes of the type [Ln(OTf)(3)] (Ln=La, Sm, Nd, Yb, Lu) serve as effective, recyclable catalysts for the rapid intramolecular hydroalkoxylation (HO)/cyclization of primary/secondary and aliphatic/aromatic hydroxyalkenes in imidazolium-based room-temperature ionic liquids (RTILs) to yield the corresponding furan, pyran, spirobicyclic furan, spirobicyclic furan/pyran, benzofuran, and isochroman derivatives. Products are straightforwardly isolated from the catalytic solution, conversions exhibit Markovnikov regioselectivity, and turnover frequencies are as high as 47 h(-1) at 120 degrees C. The ring-size rate dependence of the primary alkenol cyclizations is 5>6, consistent with a sterically controlled transition state. The hydroalkoxylation/cyclization rates of terminal alkenols are slightly more rapid than those of internal alkenols, which suggests modest steric demands in the cyclic transition state. Cyclization rates of aryl-functionalized hydroxyalkenes are more rapid than those of the linear alkenols, whereas five- and five/six-membered spirobicyclic skeletons are also regioselectively closed. In cyclization of primary, sterically encumbered alkenols, turnover-frequency dependence on metal-ionic radius decreases by approximately 80-fold on going from La(3+) (1.160 A) to Lu(3+) (0.977 A), presumably reflecting steric impediments along the reaction coordinate. The overall rate law for alkenol hydroalkoxylation/cyclization is v approximately k[catalyst](1)[alkenol](1). An observed ROH/ROD kinetic isotope effect of 2.48 (9) is suggestive of a catalytic pathway that involves kinetically significant intramolecular proton transfer. The present activation parameters--enthalpy (DeltaH(++))=18.2 (9) kcal mol(-1), entropy (DeltaS(++))=-17.0 (1.4) eu, and energy (E(a))=18.2 (8) kcal mol(-1)--suggest a highly organized transition state. Proton scavenging and coordinative probing results suggest that the lanthanide triflates are not simply precursors of free triflic acid. Based on the kinetic and mechanistic evidence, the proposed catalytic pathway invokes hydroxyl and olefin activation by the electron-deficient Ln(3+) center, and intramolecular H(+) transfer, followed by alkoxide nucleophilic attack with ring closure.

show abstract

Section: A C H T U N G T R E N N U N G [Alkenol]mentioning

confidence: 99%

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

Dzudza

Marks

2010

Chemistry A European J

Self Cite

View full text Add to dashboard Cite

show abstract

“…The search for a specific metal catalyst for hydroalkoxylation [4a, 5-7] of nonactivated alkenes, using the reaction of Scheme 1 as a model reaction, was initiated by a 1998 report on a ruthenium triflate catalyst. [18][19][20] Since then, numerous similar reports on catalysis with ZrCl 4 , [21] Sn(OTf) 4 , [22] Al(OTf) 3 , [23] Cu(OTf) 2 or AgOTf, [24] Ln(OTf) 3 in ionic liquids, [25,26] or with Au(PPh 3 )OTf [27] have appeared. Related catalysts were also reported for the tandem conversion of allyl aryl ethers, via 2-allylphenols to coumarans.…”

Section: Introductionmentioning

confidence: 99%

Aluminum‐Catalyzed Hydroalkoxylation at Elevated Temperatures: Fast and Simple Access to Coumarans and Other Oxygen Heterocycles

2013

View full text Add to dashboard Cite

An aluminum‐catalyzed intramolecular hydroalkoxylation of nonactivated alkenes is presented as a powerful synthetic tool for the preparation of oxygen heterocycles, which are of major interest for the preparation of biological and pharmaceutical active compounds. The aluminum isopropoxide catalyzed (5 mol %) cyclization of 2‐allylphenols at elevated temperatures (250 °C, 20 min) provides 2‐methylcoumarans (2‐methyl‐2,3‐dihydrobenzofuran) in an exceptionally fast, simple, and economic manner. Moreover, heating of allyl aryl ethers with aluminum isopropoxide (5 mol %) gives 2‐methylcoumarans by a tandem Claisen rearrangement–hydroalkoxylation reaction. For either reaction, the catalyst tolerates a broad scope of substrates with various functional groups. By using the weakly electrophilic aluminum alkoxide as the catalyst, occurrence of “hidden Brønsted acid” catalysis can be excluded under the present reaction conditions.

show abstract

“…The hydrothiolation of 1-heptyne with PhSH (2 equiv) was catalyzed by Ni (acac) (2 mol%) at 40 C under solvent-free conditions to produce 9, 10, and 11 in 81%, 4%, and 4% yields, respectively (7). In the reaction, the formation of an insoluble dark brown polymer [Ni(SAr) 2 ] n was confirmed by elemental analysis [28], and it was verified that the polymer served as the catalyst for the reaction of HCCC(OH)Me 2 with PhSH to give the corresponding Markovnikov-type product in 95% yield.…”

Section: Ni(ii)-catalyzed Hydrothiolation and Hydroselenationmentioning

confidence: 99%

The Mechanism for Transition-Metal-Catalyzed Hydrochalcogenation of Unsaturated Organic Molecules

Ishii

Nakata

2011

Hydrofunctionalization

View full text Add to dashboard Cite

In this chapter, discussions are focused on two types of mechanisms of transition-metal-catalyzed hydrochalcogenation, Type I and Type II, which are classified by the initial behavior of precatalysts. In Type I mechanism, precatalyst M-X (M ¼ Pd, Ni, Zr, Ln, and An) first undergoes protonolysis with REH (E ¼ O, S, and Se) to generate active catalyst M-ER, which then undergoes insertion of alkyne into the M-ER bond (chalcogenometalation) to give 2-chalcogenovinyl complex, followed by protonolysis of M-C vinyl with REH to produce the product and to regenerate active catalyst M-ER. Type II mechanism starts from oxidative addition of REH (E ¼ S and Se) to

show abstract

Efficient Intramolecular Hydroalkoxylation/Cyclization of Unactivated Alkenols Mediated by Lanthanide Triflate Ionic Liquids

Cited by 89 publications

References 50 publications

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

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

Aluminum‐Catalyzed Hydroalkoxylation at Elevated Temperatures: Fast and Simple Access to Coumarans and Other Oxygen Heterocycles

The Mechanism for Transition-Metal-Catalyzed Hydrochalcogenation of Unsaturated Organic Molecules

Contact Info

Product

Resources

About