Letters in Organic Chemistry - Volume 3, Issue 12, 2006

The cyclization of 4,5-dihydroxy-2-methyl-pyrimidine followed by dibromination and oxidation of the methyl group led to 6,7-dihydro-[1,4]dioxino[2,3-d]pyrimidine-2-carboxaldehyde. This compound underwent different chemical transformations on carbonyl group to synthesize various 2-substituted-6,7- dihydro-[1,4]dioxino[2,3-d]pyrimidines.

New pseudopeptides possessing C2 symmetry and dihydroxyethylene core derived from (R,R)- tartaric acid and amino esters have been synthesized as potential inhibitors of HIV protease. The amino esters were chosen in order to interact with P1/P1' and P2/P2' subsites of the enzyme. The products were obtained in good yields without noticeable racemization.

Ultrasonic irradiation effectively promotes the 1,3-dipolar cycloaddition reaction of azomethine ylides generated from L-phenyl alanine and isatin derivatives via the decarboxylative with N-aryl maleimides in aqueous solution under stereoselective cycloaddition via endo-transition state to give new spiro pyrrolidine cycloadducts.

The synthesis of various original vinylic chlorides from trichloromethylated substrates in the quinoline series is described herein. This reaction takes place under mild operating conditions via a monoelectronic transfer mechanism and presents elevated yields.

A novel one-pot synthesis was developed for the preparation of partial amide esters of (dichloromethylene)bisphosphonic acid from readily available tetramethyl ester with good selectivity and purity.

For the first time, Baker's yeast immobilized mesoporous MCM-41 (BY/MCM-41) is put forward as a promising heterogeneous catalyst for selective reduction of aromatic nitro and carbonyl containing compounds. The catalyst is highly efficient for the reduction of aromatic nitro and carbonyl groups to their respective amines and alcohols. It showed highly regio- and chemoselectivity for the reduction of substituted aromatic di Read More

The first convergent and non-protective synthesis of a G-2 melamine dendrimer having (1S,2S)-1,3- dihydroxy-1-(4-nitrophenyl)-prop-2-ylamino units as peripheral groups (from l-p-nitrophenylserinol) and piperazine as linker is described to occur in five linear steps and 27% overall yield. The restricted rotation about Csp2(s-triazine)-N(exocyclic) bonds, exhibited by all compounds, is discussed as relevant.

A series of cholesterylated carboxylic acids L1-L6 as the hepatic targeting ligands were synthesized for gene delivery. The characteristics of those ligands is cholesterylated ones with different spacer lengths with oigo(ethylene glycol) units. We designed two different routes to synthesize L1-L6 from alcohol 3 under mild condition in moderate yield.

Pyrimidinone, thioxopyrimidinone, pyrimido[2,1-a]phthalazinone and [1,3]oxazino[2,3-a] isoindolone were obtained by means of microwave-assisted [4+2] cycloreversion. The microwave heating of the parent norbornene or oxanorbornene fused compounds in a solvent with a medium or large loss factor generates retro Diels-Alder products in excellent yield and high purity.

The cycloaddition reaction of non-stabilized azomethine ylides towards (E)-3-arylidene-4- flavanone, (E)-3- arylidene-4-chromanone and (E)-2-arylidene-1-tetralone as dipolarophiles has been investigated. High degree of regioselectivity has been observed in the synthesis of a new class of functionalised dispiroheterocyclic compound containing dispiro pyrrolo-isoquinoline and acenaphthequinone framework.

(R)-Arundic acid 15 was prepared in a simple manner and with absolute optical purity via Cu and Fe mediated and Luche's crotylation of 1 with bromides 6a,b. Co wasn't a good mediator for these crotylation reactions. The stereoselectivity for all crotylations were similar producing mainly 7b, c, besides a small amount of 7a.

The catalytic system generated from ionic liquids, simple copper salts and terminal oxidant tertbutyl hydroperoxide provided an efficient protocol for the allylic oxidation of ionone-like dienes to corresponding enones. Optimal conditions, short reaction time, and good yields were obtained. Copper nanoparticles were found to be effective catalysts for the oxidation by TEM.

Several monosaccharides were peracetylated in excellent isolated yields (89-100%) with vinyl acetate in aqueous Na3PO4. The per-O-acetylation reaction is fast and mild, as well as insensitive to water. Meanwhile, the workup is convenient and the catalyst can be recycled easily.

In the present paper it is described the use of hexamethylenetetramine combined to the use of bmim+ type ionic liquids as cheap, environmentally friendly and efficient catalytic systems for Baylis- Hillman reactions between aromatic aldehydes and acrylonitrile or methyl acrylate. The Baylis-Hillman adducts were obtained in moderate to good yields (50-85%), in short reaction times. The ionic liquids can be recycled.

Chloroacetic (1a), dichloroacetic (2a) and acetic acid (3a) were prepared by direct transformation of trichloroethylene, tetrachloroethylene and 1,1-dichloroethylene, respectively, using sulfuric acid in the presence of catalytic amounts of crown ethers. The newly developed method increases the reaction rate by suppressing the formation of by-products, and 1a, 2a and 3a were obtained in good yields at decreased reaction tempe Read More

Over the past ten years polymer-supported reagents and scavengers have been widely employed in organic chemistry. The same period of time also saw the advent of microwave assisted synthesis. A combination of these technologies can be beneficial to the redesign of classical reactions. In this work we present a series of examples for the widely known Friedel-Crafts reaction and for the Krohnke-King-Ortoleva reaction.

The efficient synthesis of sterically demanding tetra-substituted biaryls by means of a one-pot threestep low-temperature modification of the classical Ullmann reaction is reported. The major benefit of this methodology lies in the ready synthesis of polybrominated biaryls, which can be subsequently functionalized into various target molecules by means of regioselective halogen/metal permutations.