Yung-Son Hon

The mechanistic study and synthetic applications of the base treatment in the ozonolytic reactions

Abstract The E1cb mechanism is the overwhelming process in the reaction of bases and ozonides. As a quenching agent in the ozonolysis of a variety of alkenes, the reactions involving triethylamine often gave better yields and proceeded faster than those involving methyl sulfide. On the other hand, in the presence of 4 A molecular sieves, the secondary amines reacted with mono- and 1,1-di-substituted ozonides to afford the reductive amination products in high yields. The formation of ammonium formate in the reaction mixture also supported the E1cb mechanism in the reaction of ozonide and amine.

Dibromomethane as one-carbon source in organic synthesis: microwave-accelerated α-methylenation of ketones with dibromomethane and diethylamine

The reactivity of aryl alkyl ketone with a preheated mixture of dibromomethane and diethylamine is poor and gives an α-methylenation product in very low yield even under refluxing condition. It can be accelerated dramatically by microwave irradiation. Under microwave condition, the cyclic 1,3-dicarbonyls, aryl alkyl ketones, heteroaryl alkyl ketones and acyclic benzyl ketone give α-methylenation products in modest to good yields.

A Convenient and Efficient Workup of Ozonolysis Reactions Using Triethylamine

Abstract Comparison were made between triethylamine and methyl sulfide for their use as a quenching agent in the ozonolysis of a variety of alkenes. The reactions involving triethylamine often gave better yields and proceeded faster than those of involving methyl sulfide. The role of triethylamine played as base instead of reducing agent in the reaction.

Acetonyltriphenylphosphonium bromide in organic synthesis: An extremely efficient catalyst for the protection and deprotection of alcohols as alkyl vinyl ethers

Abstract Acetonyltriphenylphosphonium bromide (ATPB) was an extremely effective catalysts in the preparation of THP, THF, and EE ethers as well as cleavage of THP, THF, and EE ethers to the corresponding alcohols. It could be applied to 1°, 2° and 3° alcohols and phenol.

Single-step approach to β-cyclodextrin-bonded silica as monolithic stationary phases for CEC

A novel single-step sol-gel approach for the preparation of beta-CD-bonded silica monolithic electrochromatographic columns is established. The porous silica networks were fabricated inside fused-silica capillaries using sol-gel processing of tetramethoxysilane and an organfunctional silicon alkoxide that contains beta-CD. Scanning electron micrographs and nitrogen adsorption-desorption data showed that these functional monolithic columns have double pores structures with micrometer-size co-continuous through-pores and silica skeletons with open mesopores. The beta-CD monolithic columns have successfully been applied to the separation of several neutral and negatively charged isomers by CEC. The column performance was evaluated by using positional isomers of naphthalenedisulfonic acid as model compounds. A plate height of less than 10 mum for the first eluted isomer of naphthalenedisulfonic acid was obtained at an optimal flow rate (0.47 mm/s) of the mobile phase. Moreover, the columns have been proved to be stable for more than 100 runs during 3 months period and show reasonable column reproducibility.

Acetonyltriphenylphosphonium bromide in organic synthesis: a useful catalyst in the cyclotrimerization of aldehydes

Abstract Acetonyltriphenylphosphonium bromide (ATPB) is a useful catalyst for the cyclotrimerization of the aliphatic aldehydes under solvent-free condition. The aldehydes tethered with a variety of functionality such as olefin, ether, ester, bromide, azide and diester could also be cyclotrimerized under the catalysis of ATPB.

Preparation of α-substituted acroleins via the reaction of aldehyde or the corresponding ozonide with dihalomethane and diethylamine

Abstract Treatment of aldehydes or the corresponding ozonides with a mixture of dibromomethane and diethylamine afforded α-substituted acroleins in modest to good yields. The β-carbon of the acrolein ( nc , n = 1–16) derived from dibromomethane. Functional groups, such as ketone, hydroxy, acetoxy, bromide, iodide, ester are compatible with this reaction condition. The relative rates and yields of this transformation in dichloromethane were found to be in the following order: CH 2 I 2 > CH 2 Br 2 > CH 2 Cl 2 .

Syntheses of (2S, 4S)- and (2S, 4R)-4-substituted glutamic acid analogues for neuroexcitatory activity studies

The stereospecific syntheses of various length of 4(R)- and 4(S)-substituted 2(S)-glutamic acid were described

A novel NMDA receptor antagonist protects against N-methyl-d-aspartate- and glutamate-induced neurotoxicity in the goldfish retina

4(R)-(3-Phenylpropyl)-2(S)-glutamic acid, C(3), is a synthetic analogue of L-glutamate. This analogue reversibly inhibits the membrane depolarization of neurons in the CA1 region of rat hippocampal slices evoked by N-methyl-D-aspartate (NMDA), with an EC50 value of 3.6 microM, whereas the depolarization of these neurons evoked by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid is not inhibited by C(3). Analyses of the inhibitory effect of C(3) on NMDA-evoked currents of dissociated rat hippocampal neurons further revealed that C(3) acts as a competitive antagonist of NMDA receptors and that the inhibitory action of C(3) is not use-dependent. Using goldfish retina as a model, we found that the neuronal damage produced by glutamate or by NMDA was effectively prevented by C(3). Incubation of retinas with high concentrations of C(3), up to 1 mM, did not induce pathomorphological changes in retinal neurons. These results suggest that C(3) is a useful neuroprotectant against excitotoxic damage of neurons.

Syntheses of bifunctional compounds from cycloalkenes via ozonide intermediates

Abstract The ozonolytic cleavage of cycloalkene in the presence of methyl pyruvate affords a tri-substituted ozonide. The resulted tri-substituted ozonide moiety contained three reactive centers (i.e. peroxide, ozonide ring proton and methoxycarbonyl group) which could be transformed to different functional groups under different conditions in good yields. It is a very efficient and versatile methodology to prepare the terminal differentiated compounds from symmetric cycloalkenes in two steps in high yields.