Categories: Synthesis of O-Heterocycles >
Synthesis of 3,4-dihydro-2H-pyrans
Recent Literature
An olefin metathesis/double bond migration sequence of allyl ethers to cyclic
enol ethers is catalyzed by first and second generation Grubbs' catalysts. These
ruthenium carbene complexes were activated to catalyze the double bond migration
by additioin of hydride sources, such as NaH or NaBH4.
B. Schmidt, Eur. J. Org. Chem., 2003, 816-819.
Molecular iodine catalyzes practical and mild syntheses of
substituted pyrans and furans under solvent-free conditions at ambient
temperature and atmosphere, thus offering a facile and practical alternative to
currently available reaction protocols. A combination of experimental studies
and density functional theory calculations revealed interesting mechanistic
insights.
D. P. Pace, R. Robidas, U. P. N. Tran, C. Y. Legault, T. V. Nguyen, J. Org. Chem., 2021, 86,
8154-8171.
A titanocene-catalyzed reductive domino reaction provides gem-difluorobishomoallylic
alcohols starting from trifluoromethyl-substituted alkenes and epoxides.
Furthermore, diverse 6-fluoro-3,4-dihydro-2H-pyrans have been prepared
through derivatization of the cross-coupling products in a single step.
Z. Lin, Y. Lan, C. Wang,
Org. Lett., 2020, 22, 3509-3514.
The carbonyl ene reaction of 2-methylenetetrahydropyrans provides
β-hydroxydihydropyrans under mild conditions in very good yields. This synthesis
of 2-substituted tetrahydropyrans enables a direct introduction of oxygen
heterocycles into molecular frameworks.
G. Liang, D. T. Sharu, T. Lam, N. I. Totah, Org. Lett., 2013,
15, 5974-5977.
C2-symmetric bis(oxazoline)-Cu(II) complexes catalyze the
inverse electron demand hetero Diels-Alder reaction of α,β-unsaturated carbonyl
compounds with electron-rich olefins in high diastereo- and enantioselectivity.
α,β-Unsaturated acyl phosphonates and β,γ-unsaturated α-keto esters and amides
are effective heterodienes, while enol ethers and sulfides function as
heterodienophiles.
D. A. Evans, J. S. Johnson, E. J. Olhava, J. Am. Chem. Soc., 2000,
122, 1635-1649.
Hydrophobic ionic liquids such as [Bmim]PF6 are powerful media for
bis(oxazoline)-copper-catalyzed asymmetric hetero-Diels-Alder reactions, that
allow a convenient catalyst recycling. The reactivities and stereoselectivities
were comparable to those of the corresponding homogeneous reactions. Furthermore,
the reaction was remarkably accelerated in [Bmim]PF6 compared to
dichloromethane.
Y. J. Shin, C.-E. Yeom, M. Jeong, B. M. Kim, Synlett, 2008,
89-93.
Tuning the reactivity of arylpalladium intermediates enables 5-exo and 6-endo
cyclizations of alkynols. These palladium-catalyzed reactions offer a divergent
synthesis of oxygen-containing heterocycles, which are of synthetic use for
further derivatization. Formal synthesis of an hNK-1 receptor antagonist also
showcases the utility this arylative cyclization.
D. Fujino, H. Yorimitsu, A. Osuka, J. Am. Chem. Soc., 2014,
136, 6255-6258.
The combination of IPrAuCl and NaBArF catalyzes an efficient synthesis of
functionalized volatile oxa-bicyclo[4.1.0]-hept-4-ene compounds in good yields.
The utility of these low-molecular-weight enols was demonstrated by
derivatization of some adducts and olfactory evaluation.
R. Laher, C. Marin, V. Michelet,
Org. Lett., 2020, 22, 4058-4062.