Bio-Availability of Biotin in Cereals

The decomposition of acid azides to isocyanates and nitrogen is known as the Curtius rearrangement The reaction is a preparative method for isocyanates, ureas, amides, and amines When coupled with a hydrolytic step, the Curtius rearrangement becomes a practical procedure for replacing a carboxyl group by an amino group The overall process of converting an acid through its azide to an amine is commonly referred to as the Curtius reaction Acid azides are commonly prepared by treating hydrazides in cold, aqueous solution with nitrous acid Azides can be rearranged in inert solvents, from which isocyanates can be isolated in the presence of water or alcohol, which will react with the intermediate to form urethans or ureas


Keywords:

curtius reaction;
monocarboxylic acids;
unsaturated acids;
hydroxy acids;
keto acids;
amino acids;
functional groups;
heterocyclic systems;
azides;
Hofmann reaction;
Schmidt reaction;
related reactions;
experimental procedures

The Curtius Reaction

Aminothiophenes and their Derivatives

The Dieckman condensation is an acetoacetic ester condensation in which a dicarboxylic ester is cyclized to a beta-ketonic ester through the action of a base. The dicarboxylic ester must have at least one alpha-hydrogen atom and the carbalkoxy groups must be situated that cyclization will result in a 4-membered ring or larger ring. Discovery and development of the reaction are generally credited to Dieckmann, who found that heating an adipic or a pimelic ester with sodium and a trace alcohol led to cyclization with formation of a cyclopentanone or a cyclohexanone. The Dieckmann condensation has proved useful for the preparation of a variety of carbocyclic and heterocyclic ketones and has been extended to the synthesis of 7 and 8-membered rings.


Keywords:

Dieckman condensation;
cyclizations;
Michael condensation;
intermolecular ester;
alkylation;
acyloin condensation;
failures

The Dieckmann Condensation (Including the Thorpe‐Ziegler Condensation)

Thiophenes and tetrahydrothiophenes are discussed as separate major divisions in this chapter because there are significant differences in the general methods by which these two similar types of compounds are prepared. The general reactions that lead to the formation of thiophenes may be segregated in the following five general classifications (1) Reaction of the 1,4-difunctional compounds with sulfides; (2) reaction of unsaturated compounds with sulfides; (3) reaction of 1,2-difunctional compounds with thiodiacetic acid and esters; (4) reaction of aryl methyl ketones with sulfides; (5) miscellaneous cyclization reactions. Similarly the reactions that form tetrahydrothiophenes may be grouped into four general classifications: (1) Reaction of 1,4-difunctional compounds with sulfides; (2) Dieckmann cyclization; (3) Catalytic method; (4) miscellaneous methods. All of the above are discussed in this chapter.


Keywords:

thiophenes;
tetrahydrothiophenes;
sulfides;
succinic acids;
1,4-Difunctional compounds;
1,2-Difunctional compounds;
experimental procedures

L. C. Cheney

Papers

The total synthesis of 2, 3, 4, 5-tetradehydrobiotin.