Synthesis of O-Heterocycles

Synthesis of
Cyclic ethers	Lactones	Acetals	Oxathioacetals
Dioxolanones	Oxazolidinones	Butenolides	3(2H)-Furanones Benzofuranones
2,5- Dihydrofurans	2,3- and 4,5- Dihydrofurans	Furans, (Di)Benzofurans
Oxazoles Benzoxazoles	Isoxazoles	1,3,4- Oxadiazoles	1,2,4- Oxadiazoles
2H-Pyrans and Benzopyrans	3,4-Dihydro- 2H-pyrans
Chromanones	Chromones, Flavones	Coumarins	Isocoumarins

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Recent Literature

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.

Addition of a catalytic amount of Cy₂NH·HX improves the rate and yields for cyclization reactions of o-(alkynyl)benzoates in the presence of a stoichiometric amount of copper(II)halide to give 4-haloisocoumarins. Under the standard reaction conditions, various 4-haloisocoumarins are provided in good yield.
Y. Liang, Y.-X. Xie, J.-H. Li, Synthesis, 2007, 400-406.

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 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.

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.

A chiral Ti(IV) catalyst can be successfully utilized in the asymmetric 1,3-dipolar cycloaddition reactions between various nitrones and acrolein to give the corresponding endo cycloadducts (isoxazolidines) with high to excellent enantioselectivities.
T. Kano, T. Hashimoto, K. Maruoka, J. Am. Chem. Soc., 2005, 70, 11926-11927.

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.

A three-component condensation gave 2-amino-4H-1,3-oxazines or 2-amino-4H-1,3-thiazines from alkynes, urea or thiourea, and aldehydes.
S. Huang, Y. Pan, Y. Zhu, A. Wu, Org. Lett., 2005, 7, 3797-3799.

Stereocontrolled Construction of O-Heterocycles Asymmetric Hetero-Diels-Alder Reactions O-Heterocyclic Construction by Alkene Metathesis Stereoselective Construction of Oxygen Heterocycles