Current Organic Synthesis - Volume 1, Issue 4, 2004

The isolation and biological activity of carbazole alkaloids is summarized. Recent developments of novel methodologies for the synthesis of carbazole alkaloids are described. The focus is on syntheses using the oxidative coupling of arylamines with either arenes, cyclohexadienes, or cyclohexene mediated or catalyzed by palladium, iron, or molybdenum. The implementation of these annulations in total syntheses provides highly convergent routes to biologically active carbazole alkaloids. Advantages, scope, and limitations of the different synthetic methods are discussed.

Niobium pentachloride has proved to be a powerful activating agent for various organic reactions. This oxophylic reagent possesses a good Lewis acidity and has received increasing attention in recent years. Different outcomes from more common Lewis acids have been achieved in some reactions. In this review, the applications of this versatile reagent in organic synthesis will be disclosed.

This review summarizes the different synthetic methods for the preparation of vinylphosphonates based exclusively on the use of transition metal complexes as promoters, i.e. employed in stoichiometric or catalytic amounts.

The synthesis of phosphonic and phosphinic derivatives comprises the use of the corresponding phosphorus chlorides. A novel approach applies low-coordinated P-species, methylenephosphine oxides (YP(O)CH2, Y =Ar, alkyl, alkoxy), which can be generated by the fragmentation of bridged P-heterocycles, 2- phosphabicyclo[2.2.2]oct-5-enes available by Diels-Alder cycloadditions. The fine tuning between the structure and reactivity of different type of precursors is discussed. Thermolysis or photolysis of the suitable phosphabicyclooctenes in the presence of hydroxy compounds or amines affords a rich variety of phosphinic or phosphonic derivatives. The potential of the photolysis is that it requires mild conditions (26°C) and that it is highly efficient.

The preparation of 4-alkoxy-1,1,1-trichloro-3-alken-2-ones (enones), important synthetic tools for the heterocyclic synthesis, from cheap and easily accessible starting materials, is reported. The applications of the enones in the synthesis of isoxazoles, pyrazoles, pyrimidines and other heterocycles are also reported. This review was grouped into two main sections: (i) synthesis of 4-alkoxy-1,1,1-trichloro-3-alken-2-ones and derivatives and (ii) applications of 4-alkoxy-1,1,1-trichloro-3-alken-2-ones in heterocyclic synthesis.

With the advent of green chemistry, the importance of environmentally benign synthesis has been increasingly recognized. This review summarizes recent progresses in this field, covering mainly the organocatalysis, lanthanide triflate catalysis, and our recent related works. Emphasis will be paid on synthetic applications and their significance to green technology by using environmentally friendly reagents and solvents such as water and ionic liquids. In addition, some new trends in the related areas such as chemoenzymatic catalysis and organic synthesis in ionic liquid will be discussed.