Letters in Organic Chemistry - Volume 5, Issue 4, 2008

The chiral amino alcohol HOC6H4CH(NH2)C(C6H5)2OH (4) that is derived from (R)-4-hydroxyphenylglycine has been converted into novel soluble and insoluble polymer-bound reagents 5. After in-situ conversion into oxazaborolidines, they serve for enantioselective reductions of acetophenone to deliver (S)-1-phenylethanol (6) in up to 83% enantiomeric excess.

The irradiation of chiral phenylglyoxylate esters in the presence of furan within NaY, LiY, KY, CsY, and RbY showed in some cases an increase of stereoselectivity in comparison with the observed stereoselectivity when the reaction was performed in solution. The enhanced stereoselectivity can be explained assuming that the biradical intermediate of the reaction can have an advantage (it occupies a smaller volume) to assume the correct conformation able to cyclize when the reaction is performed within a zeolite. This advantage is greater for the stereoisomer able to give the observed product than for the other one. In the case of the phenylglyoxylate ester obtained from (S)-1-methyl-1-propanol, the stereoselectivity was higher with NaY than with LiY. In the case of the phenylglyoxylate ester obtained from (S)-2-methyl-1-butanol, NaY and LiY gave the same stereoselectivity. The effect of the cation can be explained considering that, in the case of the phenylglyoxylate ester obtained from (S)-1-methyl-1-propanol, the interaction between the LUMO of the alkali ion and the HSOMO of the biradical intermediates was different for SS and RS stereoisomers. In the case of the phenylglyoxylate ester obtained from (S)-2-methyl-1-butanol no difference was observed in the HSOMO of SS and RS stereoisomers of the biradical intermediates in agreement with the observed no effect of the change of alkali ions. When the reaction was performed within β-cyclodextrin a reduction of stereoselectivity was observed.

The use of aryl vinyl ketones in the Heck reaction for the synthesis of flavonoids was previously described. Herein we present our preliminary study on the reactivity of aroyl alkynes or propargyl alcohols in the Heck-Sonogashira- Cassar coupling reactions to obtain alkynyl precursors of flavones. This procedure envisaged a general protocol for the synthesis of variously substituted flavones.

The fluoride and thioglycoside derivatives of 6-thiosialic acid were synthesized. The thioglycoside was found to react with glycosyl acceptors in the presence of N-iodosuccinimide and trifluoromethanesulfonic acid. Alkanols tended to be glycosylated in good yield with α-selectivity, while sugar alcohols gave only the β-glycosides in poor yields.

A short and facile synthesis of bis-Betti bases with two chiral carbon centers was achieved firstly. The structures were established on the basis of IR, elemental analysis, 1HNMR, and one of the products was confirmed by a singlecrystal X-ray diffraction analysis.

The isomeric distributions of some cyclohexenyl enamines substituted by succinyl or acetyl groups at either the 2- or 6-positions are reported as are the isomeric distributions of similarly substituted cyclopentenyl enamines. Correlation between the 13C NMR chemical shifts in these enamines and isomer distribution is shown. Density functional molecular modeling is used to demonstrate resonance and electrostatic effects on isomeric distributions.

A simple convergent regioselective synthesis of hitherto unreported coumarin- and quinolone-annulated heterocycles in excellent yields has been achieved by the palladium-catalyzed intramolecular Heck reaction.

An efficient one-pot procedure was developed for the synthesis of 4,6-diaryl-2-pyridinones and 4-aryl-8- arylidene-5,6,7,8-tetrahydro-2- quinolinones based on cyclocondensation reactions of N-ethoxycarbonylmethylpyridinium chloride or N-carbamoylmethyl pyridinium chloride with aromatic aldehydes and substituted acetophenones or cyclohexanone. The multi-component reaction is performed by microwave irradiation with the reaction substances in the system of NH4OAc/HOAc.

The Henry reaction has been efficiently catalyzed by a Cd-proline complex in water at ambient temperature to afford the β-nitroalcohols in good to excellent yields. Effective recovery and recycling (up to five runs) of the catalyst are documented.

An efficient and expeditious direct protocol for the preparation of amidoalkyl naphthols employing a multicomponent, one-pot condensation reaction of 2-naphthol, aromatic aldehydes and acetonitrile or acetamide in the presence of alumina sulfuric acid as a solid heterogeneous acid catalyst under solvent, solvent-free and microwave conditions has been described.

2-Carbethoxy-6-acetylpyridine and 2,6-diacetylpyridine were transformed in good yields from the reaction of 2,6-dicarbethoxypyridine and EtOAc in the presence of sodium along with/without an equivalent of ethanol to sodium in toluene. The β-keto esters, the intermediates in the transformation of β-keto carboxylate into acetyl group, were isolated for understanding the plausible mechanism.

Nano ceria supported on vinyl pyridine polymer was found to be an effective and reusable catalyst for the synthesis of bis(indolyl)methanes at room temperature in a protic solvent.

The novel materials, polyHIPEs with incorporated tetrasubstituted ammonium cationic surfactant (CTAB) have been applied to a broad range of radical precursors in various free radical transformations in organic and aqueous media. The advantage of this reagent/ solid phase surfactant combination lies in its affordability, miniscule toxicity, avoidance of highly toxic “tin based hydrogen donors” under green reaction conditions.

Mn(III) Schiff-base complex as a catalyst with H2O2 was applied for oxidative deprotection of THP ethers to the corresponding carbonyl compounds and conversion of silyl ethers into the parent alcohols under mild conditions. Chemoselective cleavage of trimethylsilyl ethers in the presence of t-butyldimethylsilyl ethers and cleavage of trimethylsilyl ethers in the presence of tetrahydropyranyl ethers were also achieved with this system.

Two novel stigmasterol-based cationic lipids, Stigmasta-5,22-dien-3-ol,4-[[2- (dimethylamino)ethyl]amino]-4- oxobutanoate,(3β,22E)-(9CI) and stigmasta-5,22-dien- 3-ol,4-[[2-(dimethylamino)ethyl]amino](2E)-4-oxobutenoate, (3β,22E)-(9CI), were synthesized. These compounds were characterized by mass spectrometry (MS), nuclear magnetic resonance (NMR) and fourier transform infrared (FT-IR).

An efficient one-step conversion of 4-phenyl-5-ethoxycarbonyl-3-cyano-6-metlyl-2(1H)-pyridone (1) into ethyl 3-amino-6-methyl-4-phenyl-1H-pyrazolo[3,4-b]pyridine-5-carboxylate (7) is described. An unusual hydrazine mediated decarboxylation of 7 into 3-amino-6-methyl-4-phenyl-1H-pyrazolo[3,4-b]pyridine (8) is reported. The structure of 8 was confirmed by spectral and chemical investigations. A plausible reaction mechanism for the formation of the unexpected product 8 is proposed.

A simple and efficient method for the synthesis of spirooxindoles derivatives by one-pot reactions of isatins, activated methylene reagents and activated carbonyl compounds in water under microwave irradiation was reported. This protocol has the advantages of short reaction time, high yields, easy work-up procedure and environmentally benign characters.

Chemical investigation of the leaves of Viburnum fordiae Hance has resulted in the isolation and characterization of a novel phenolic glycoside fordioside (1), and three known phenolic glycosides including stilbene glycoside and lignan glycoside (2-4). These structures were established on the basis of analysis of spectroscopic evidence. The antioxidant activities of all phenolic glycosides were also evaluated.