APPLICATIONS OF MICROWAVE ENERGY IN ORGANIC CHEMISTRY. A REVIEW

Microwave specific Wolff rearrangement of alpha-diazoketones and its relevance to the nonthermal and thermal effect

alpha-Diazoketones possess high electric dipole moments, as a consequence of the dipolar nature of the diazocarbonyl functional group. The vectorial analysis, theoretical calculations (PM3 and ab initio), and literature reports based on experimental and theoretical calculations reveal a higher dipole moment for the Z-configuration of the diazo functional group. Microwave irradiation of alpha-diazoketone (1a-m) (Figure 1) promotes Wolff rearrangement specifically via the Z-configuration in excellent yields. The dielectric properties of the solvent govern the course of the microwave rearrangement. 3-Diazocamphor (1m) on microwave irradiation in benzylamine exhibits nonthermal effects to furnish exclusively the Wolff rearrangement product (4m), equivalent to its photochemical behavior. In the presence of an aqueous medium, through solvent heating predominates, leading to the formation of a tricyclic ketone (5) as the principal product, arising from an intramolecular C-H insertion. This behavior is similar to its known thermal and transition metal catalyzed reactivity pattern.

Efficient, Solvent-Free Oxidation of Organic Compounds with Potassium Dichromate in the Presence of Lewis Acids

The synthetic utility of potassium dichromate in the presence of Lewis acids under solid phase conditions is described. This reagent efficiently oxidizes alcohols, acyloins, oximes and semicarbazones to their corresponding carbonyl compounds, while trimethylsilyl and tetrahydropyranyl ethers, ethylene acetals and ketals undergo oxidative deprotection to produce carbonyl compounds efficiently.

Synthesis of beta-lactams from diazoketones and imines: the use of microwave irradiation

[see reaction]. The transformation of diazoketones derived from alpha-amino acids to ketenes that, in turn, react further with imines to afford beta-lactams, can be realized not only by utilizing photochemical reaction conditions but also under the action of microwave irradiation. Under the latter reaction conditions 4-alkenyl-substituted beta-lactams derived from amino acids, substrates that were not previously accessible, have been prepared. beta-Lactams possessing a trans-substitution pattern at the ring were obtained exclusively.

Benzyltriphenylphosphonium Peroxymonosulfate: As a Novel and Efficient Reagent for Oxidation of Alcohols under Solvent-Free Conditions

This paper describes the oxidation of alcohols under solvent-free conditions using benzyltriphenylphosphonium peroxymonosulfate, which has been prepared by mixing an aqueous solution of benzyltriphenylphosphonium chloride with oxone® at room temperature. This reagent is stable white powder, which may be stored for months without loss of its activity. This compound is readily soluble in organic solvents such as acetonitrile, chloroform, and dichloromethane and slightly soluble in carbon tetrachloride, ether, and hexane.

Microwave-assisted Synthesis of Triazones and 4-Oxo-oxadiazinane in Dry Media

Three component condensation of N,N-dimethylurea, paraformaldehyde and primary amines using montmorillonite K-10 in dry media under microwave irradiation leads to triazones 5a-f in high yields.

Remarkable Fast Microwave-assisted Zeolite HZSM-5 Catalyzed Oxidation of Alcohols with Chromium Trioxide under Solvent-free Conditions

A variety of alcohols are oxidized to the corresponding carbonyl compounds in excellent yields by chromium trioxide-HZSM-5 zeolite under microwave irradiation in a solventless system.

Deoximation by Pyridinium Chlorochromate under Microwave Irradiation

Regeneration of carbonyl functions from oximes can be accomplished by use of pyridinium chlorochromate under microwave irradiation within a short time with excellent yields.