Synthesis of O-Heterocycles
Highly functionalized δ-lactones were produced in the presence of a catalytic amount of the Cu(OAc)2-DIFLUORPHOS complex through three-component assembly of dialkylzincs, allenic esters, and unactivated ketones. This CAMCR (catalytic asymmetric multicomponent reaction) constructs two C-C bonds and one tetrasubstituted chiral center simultaneously.
K. Oisaki, D. Zhao, M. Kanai, M. Shibasaki, J. Am. Chem. Soc., 2007, 129, 7439-7443.
A BINOLate-zinc complex prepared in situ from Et2Zn and 3,3'-dibromo-BINOL is an efficient catalyst for the enantioselective hetero-Diels-Alder reaction of Danishefsky's diene with aldehydes to give 2-substituted 2,3-dihydro-4H-pyran-4-ones in up to quantitative yield and 98% ee.
H. Du, J. Long, J. Hu, X. Li, K. Ding, Org. Lett., 2002, 4, 4349-4352.
A new type of chromium-salen complex bearing DIANANE (endo,endo-2,5-diaminonorbornane) has been applied to the hetero-Diels-Alder reaction of Danishefskys diene with various aldehydes. The reactions afford the corresponding 2-substituted 2,3-dihydro-4H-pyran-4-ones in high yields and enantioselectivities.
A. Berkessel, N. Vogl, Eur. J. Org. Chem., 2006, 5029-5035.
A rhodium-catalyzed cycloisomerization converts various acyclic enynes to their cyclic diene isomers with endoselectivity. Two different catalyst systems have been developed, which are effective in promoting the C-C bond-forming cyclization of enynes to furnish carbo- and heterocycles in good to excellent yield. The mechanism is discussed.
H. Kim, C. Lee, J. Am. Chem. Soc., 2005, 127, 10180-10181.
A solvent- and metal-free regioselective cyclization affords 1,4-oxazine and 1,4-oxazepine derivatives as exo-dig products. Substrates for the cyclization step can be produced in a highly diastereomeric fashion by Grignard reaction as key synthetic step following Cram’s rule.
J. K. Vandavasi, W.-P. Hu, H.-Y. Chen, G. C. Senadi, C.-Y. Chen, J.-J. Wang, Org. Lett., 2012, 14, 3134-3137.
A general synthesis of various oxetan-3-ones uses readily available propargylic alcohols as substrates and proceeds without the exclusion of moisture or air. The facile formation of the strained oxetane ring provides strong support for the intermediacy of α-oxo gold carbenes. This safe and efficient generation of gold carbenes offers an entry into α-oxo metal carbene chemistry without using hazardous diazo ketones.
L. Ye, W. He, L. Zhang, J. Am. Chem. Soc., 2010, 132, 8550-8551.
An expedient and reliable method for accessing reactive α-oxo gold carbenes via gold-catalyzed intermolecular oxidation of terminal alkynes offers a safe and economical alternative to strategies based on diazo substrates. Its synthetic potential is demonstrated by expedient preparation of dihydrofuran-3-ones containing a broad range of functional groups.
L. Ye, L. Cui, G. Zhang, L. Zhang, J. Am. Chem. Soc., 2010, 132, 3258-3259.
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.
Δ3-Aryl/heteroaryl substituted heterocycles via sequential Pd-catalysed termolecular cascade/ring closing metathesis (RCM)
H. A. Dondas, B. Clique, B. Cetinkaya, R. Grigg, C. Kilner, J. Morris, V. Sridharan, Tetrahedron, 2005, 61, 10652-10666.
An effective, Ru-catalyzed cycloisomerization of benzannulated homo- and bis-homopropargylic alcohols affords benzofurans and isochromenes chemo- and regioselectively (5-, and 6-endo cyclizations). The presence of an amine/ammonium base-acid pair is crucial for the catalytic cycle.
A. Varela-Fernández, C. González-Rodríguez, J. A. Varela, L. Castedo, Carlos Saá, Org. Lett., 2009, 11, 5350-5353.
Sequential coupling-imination-annulation reactions of ortho-bromoarylaldehydes and terminal alkynes with ammonium acetate in the presence of a palladium catalyst under microwave irradiation gives various substituted isoquinolines, furopyridines, and thienopyridines in good yields.
D. Yang, S. Burugupalli, D. Daniel, Y. Chen, J. Org. Chem., 2012, 77, 4466-4472.
The electrochemically induced catalytic multicomponent reaction of cyclic 1,3-diketones, aldehydes and malononitrile in alcoholic solvents results in the formation of substituted 5,6,7,8-tetrahydro-4H-chromenes in excellent yields.
M. N. Elinson, A. S. Dorofeev, S. K. Feducovich, S. V. Gorbunov, R. F. Nasybullin, F. M. Miloserdov, G. I. Nikishin, Eur. J. Org. Chem., 2006, 4335-4339.
A regioselective one-pot synthesis of 2-alkyl-3,4-dihydro-3-oxo-2H-1,4-benzoxazines under microwave heating starts from commercially available 2-aminophenols. Base-mediated regioselective O-alkylation with 2-bromoalkanoates gives acyclic intermediates. A subsequent intramolecular amidation reaction furnishes the desired products in good yields.
W.-M. Dai, X. Wang, C. Ma, Tetrahedron, 2005, 61, 6879-6885.
An atom-economic, efficient, rapid, and highly regioselective one-pot click reaction allows the synthesis of benzo[e][1,4]oxazepin-5-ones in excellent yields. The method involves epoxide ring-opening-ring-closing cascade with anthranilic acids using neat grinding at room temperature in the presence of lithium bromide as a mild catalyst. Pure products are obtained simply by washing the reaction mixture with warm water.
A. K. Singh, R. Chawla, L. D. S. Yadav, Synthesis, 2012, 44, 2353-2358.
A nickel-catalyzed cycloaddition of aziridines with isocyanates proceeded smoothly to give iminooxazolidine derivatives in good yields. A longer reaction time allowed the isomerization of the iminooxazolidine to the corresponding imidazolidinone derivatives.
T. Munegumi, I. Azumaya, T. Kato, H. Masu, S. Saito, Org. Lett., 2006, 8, 379-382.
Stereocontrolled Construction of O-Heterocycles
Asymmetric Hetero-Diels-Alder Reactions
O-Heterocyclic Construction by Alkene Metathesis
Stereoselective Construction of Oxygen Heterocycles