Categories: Synthesis of O-Heterocycles
Synthesis of 2,5-Dihydrofurans
A new phosphoramidite is an effective chiral ligand in a palladium-catalyzed asymmetric Mizoroki-Heck reaction using benzyl electrophiles. The reaction is compatible with polar functional groups and can be readily scaled up. Several cyclic olefins worked well as olefin components.
Z. Yang, J. Zhou, J. Am. Chem. Soc., 2012, 134, 11833-11835.
In an asymmetric intermolecular Heck reaction, various cyclic olefins coupled with aryl and vinyl bromides in high enantioselectivity. Only bisphosphine oxides on a spiro backbone formed highly stereoselective Pd catalysts. The use of alkylammonium salts and alcoholic solvents were essential to promote halide dissociation from the arylpalladium intermediate.
C. Wu, J. Zhou, J. Am. Chem. Soc., 2014, 136, 650-652.
Neopentyl phosphine ligands promote Heck couplings with aryl bromides at ambient temperature. In the Heck coupling of 2,3-dihydrofuran di-tert-butylneopentylphosphine (DTBNpP) promotes isomerization to a much greater extent than trineopentylphosphine (TNpP). A similar complementary product selectivity is seen in the Heck coupling of cyclopentene.
M. G. Lauer, M. K. Thompson, K. H. Shaughnessy, J. Org. Chem., 2014, 79, 10837-10848.
Gold(III) chloride catalyzes a cyclization of functionalized α-hydroxyallenes into the corresponding 2,5-dihydrofurans with complete axis to center chirality transfer. This mild and efficient method can be applied to alkyl- and alkenyl-substituted allenes at room temperature, furnishing tri- and tetrasubstituted dihydrofurans in very good yields.
A. Hoffmann-Röder, N. Krause, Org. Lett., 2001, 3, 2537-2538.
Gold catalysis using a chiral bifunctional biphenyl-2-ylphosphine ligand provides 2,5-disubstituted 2,5-dihydrofurans from chiral propargylic alcohols as substrates in typically good yields and with good to excellent diastereoselectivities. With achiral substrates, 2,5-dihydrofurans are formed with good to excellent enantiomeric excesses.
X. Cheng, Z. Wang, C. D. Quintanilla, L. Zhang, J. Am. Chem. Soc., 2019, 141, 3787-3791.
A gold(I)-catalyzed formal [4 + 1] cycloaddition of α-diazoesters and propargyl alcohols provides various 2,5-dihydrofurans with a broad substrate scope and functional group tolerance. Preliminary mechanistic investigation indicates that this reaction most likely occurs through a 5-endo-dig cyclization of an α-hydroxy allene intermediate.
J. Wang, X. Yao, T. Wang, J. Han, J. Han, J. Zhang, X. Zhang, P. Wang, Z. Zhang, Org. Lett., 2015, 17, 5124-5127.
Allenylidene-ruthenium complexes on protonation with HOTf are rearranged to indenylidene-ruthenium complexes, which are efficient catalyst precursors for ring-opening metathesis polymerization, ring-closing metathesis and enyne metathesis of a variety of substrates.
R. Castarlenas, C. Vovard, C. Fischmeister, P. H. Dixneuf, J. Am. Chem. Soc., 2006, 128, 4079-4089.
A wide screening of substrates in ring-closing metathesis reactions reveals the great efficiency of phosphabicyclononane (phoban)-containing ruthenium-based pre-catalysts. Comparison of the catalytic activities with Grubbs' first-generation pre-catalyst illustrates the key role of the Phoban ligand.
F. Boeda, H. Clavier, M. Jordaan, W. H. Meyer, S. P. Nolan, J. Org. Chem., 2008, 73, 259-263.
Ethyl α-(1-hydroxy-1-alkyl)methylallenoates and α-(1-hydroxy-1-aryl)methylallenoates undergo an efficient and selective copper-catalyzed intramolecular hydroalkoxylation to give functionalized 3-ethoxycarbonyl-2-alkyl- and -aryl-2,5-dihydrofurans in good to excellent yields through a 5-endo mode.
S. Kim, P. H. Lee, J. Org. Chem., 2012, 77, 215-220.
Intramolecular hydroalkoxylation of a wide range of functionalized hydroxyallenic esters in the presence catalytic amounts of Ph3PAuCl and AgOTf in CH2Cl2 at 25 °C for 1 h produced selectively 2-alkyl- and aryl-3-ethoxycarbonyl-2,5-dihydrofurans in good to excellent yield by a 5-endo mode.
D. Eom, D. Kang, P. H. Lee, J. Org. Chem., 2010, 75, 7447-7450.
Conversion of unsaturated ketones and aldehydes derived from the cycloisomerization of primary and secondary propargyl diynols in the presence of [CpRu(CH3CN)3]PF6 to 1-azatrienes and a subsequent electrocyclization-dehydration provides pyridines with excellent regiocontrol.
B. M. Trost, A. C. Gutierrez, Org. Lett., 2007, 9, 1473-1476.
The reduction of various hetero- and carbocyclic aromatic compounds under ammonia free conditions uses LiDBB as a source of electrons, bis(methoxyethyl)amine (BMEA) as a protonating agent, and THF as a solvent. In contrast to Birch type conditions, the described ammonia free conditions allow the use of reactive electrophiles.
T. J. Donohoe, D. House, J. Org. Chem., 2002, 67, 5015-5018.
4-Mesityl-2,6-diphenylpyrylium tetrafluoroborate (MDPT) and 4-mesityl-2,6-di-p-tolylpyrylium tetrafluoroborate (MD(p-tolyl)PT) are highly robust photoredox catalysts, and exhibit some of the highest oxidation potentials reported. Their utility was demonstrated in the mild and efficient generation of carbonyl ylides from benzylic epoxides.
E. Alfonzo, F. S. Alfonso, A. B. Beeler, Org. Lett., 2017, 19, 2989-2992.