Organic Chemistry Portal
Organic Chemistry Highlights

Microwave Chemistry

Saturday, April 15, 2006
Doris Dallinger
Karl-Franzens-University Graz

Catalyst- and Base-Free Suzuki-Type Coupling

Jie Yan and co-workers from Zhejiang University of Technology, China, have reported on Suzuki-type couplings in water without the use of catalyst and base (Eur. J. Org. Chem. 2006, 2060. DOI: 10.1002/ejoc.200500915). Both symmetrical and unsymmetrical biaryls could be synthesized by coupling of sodium tetraphenylborate with hypervalent iodonium salts or iodanes under mild reaction conditions.

Synthesis of 1,4-Benzoxazine Scaffolds

A general protocol for the synthesis of 2-alkyl-3,4-dihydro-3-oxo-2H-1,4-benzoxazines 2 has been established by the group of Wei-Min Dai from the Hong Kong University of Science and Technology (Tetrahedron 2006, 62, ASAP. DOI: 10.1016/j.tet.2005.12.060). The first step was a reductive N-alkylation of substituted 2-aminophenols with aromatic aldehydes to obtain the N-alkylated anilines 1. Regioselective O-alkylation of 1 with 2-bromoalkanoates furnished acyclic intermediates which showed spontaneous cyclization to 1,4-benzoxazines 2. Higher temperatures (180-200 C) for the second step were necessary when electron-withdrawing groups were present at the C6 position (R1 = NO2, Cl).

One-Pot Synthesis of 1,2,4-Oxadiazoles

Mehdi Adib and co-workers from University of Tehran have disclosed a three-component one-pot reaction of nitriles, hydroxylamine and aldehydes to give 1,2,4-oxadiazoles (Tetrahedron Lett. 2006, 47, 2965. DOI: 10.1016/j.tetlet.2006.02.102). First the nitrile and hydroxylamine were reacted at 100 C for 1 min, subsequent addition of aldehyde and irradiation at 150 C for 3 min under solvent-free conditions gave oxadiazoles in excellent yields.

Synthesis of Tetracyclic β-Carbolines

The synthesis of thiohydantoin fused tetrahydro-β-carbolines has been investigated by the group of Chung-Ming Sun at the National Chiao Tung University in Taiwan (J. Comb. Chem. 2006, 8, 141. DOI: 10.1021/cc050098j). A soluble polymer-supported strategy using polyethylene glycol (PEG) resin combined with a traceless cyclative cleavage step was applied to achieve products 1 in high stereoselectivity. By employing microwave heating the thermodynamically stable trans diastereomers were obtained preferentially.

D. Dallinger, Org. Chem. Highlights 2006, April 15.