6-dehydro

Standard Heck conditions were used to introduce the dchydroalanine side-chain with 4-bromo-3-iodo-l-(4-methylphenylsulfonyl)indole[12]. Using 4-fluoro-3-iodo-l-(4-methylphenylsulfonyl)indole as the reactant, Merlic and Semmelhack found that addition of 2 eq, of LiCl or KCl improved yields in reactions carried out with 10% Pd/C as the catalyst[13]. The addition of the dehyroalanine side chain can also be done by stoichiometric Pd-mediated vinylation (see Section 11.2). A series of C-subslituled dehydro tryptophans was prepared in 40-60% yield by this method[14]. 

Use curved arrows to track electron movement in the dehydro halogenation of tert butyl chloride by sodium methoxide by the E2 mechanism J... 

Butadiene is an industrial chemical and is prepared by dehydrogena tion of butane Elimination reactions such as dehydration and dehydro halogenation are common routes to alkadienes... 

A steroid very closely related structurally to cholesterol is its 7 dehydro derivative 7 Dehydrocholesterol is formed by enzymatic oxidation of cholesterol and has a conju gated diene unit m its B ring 7 Dehydrocholesterol is present m the tissues of the skin where it is transformed to vitamin D3 by a sunlight induced photochemical reaction... 

Chlorinated Solvents. Originally, successive chlorination and dehydro-chlorination of acetylene was the route to trichloroethylene [79-01-6], C2HCI3, and perchloroethylene [127-18-4], C2C1. ... 

This route has been completely displaced, first by chlorination and dehydro-chlorination of ethylene or vinyl chloride, and more recendy by oxychlorination of two-carbon raw materials (2) (see Chlorocarbonsandchlorohydrocarbons). 

Serratia mane seem 3,4-dehydro-Pro prodegradation , thiazoline-4-carboxylate/ azetidine-2-carboxylate (transduction) 75 145... 

Whereas 2-deoxy-fortimicin A has full antibacterial activity (205), and the 2-deoxy-3-demethoxy- derivative is even more active than fortimicin A (236), the 2,5-dideoxy derivative has poor activity, as do the 2-deoxy-2-chloro and the 2,5-dideoxy-4,5-dehydro derivatives. The 2-amino-3-0-demethyl-2-deoxy analogue has quite good activity (229). 

In disproportionation, rosin is heated over a catalyst to transfer hydrogen, yielding dehydro (5) and dihydro (8) resin acids. The dehydro acids are stabilized by the aromatic ring the dihydro acids contain only an isolated double bond in place of the less stable conjugated double bonds. 

Reactions with amines at high temperatures under pressure lead to mixtures of dehydro-2-piperidinones (9) ... 

Chevron (St. James, La.) 682 Mobd-Badger ZSM-5 Fina-Badger dehydro... 

Sterling (Texas City, Tex.) 727 Monsanto AlCl Monsanto dehydro... 

The principal constituents of rosin (qv) are abietic and related acids. Tall oil (qv) is a mixture of unsaturated fatty and aHcycHc acids of the abietic family. Refined tall oil may be high in rosin acids or unsaturated acids, depending on the refining process. Ethoxylates of rosin acids, eg, dehydro abietic acid, are similar to fatty acid ethoxylates in surfactant properties and manufacture, except for thek stabiHty to hydrolysis. No noticeable decomposition is observed when a rosin ester of this type is boiled for 15 min in 10% sulfuric acid or 25% sodium hydroxide (90). Steric hindrance of the carboxylate group associated with the aHcycHc moiety has been suggested as the cause of this unexpectedly great hydrolytic stabiHty. 

The most significant chemical characteristic of L-ascorbic acid (1) is its oxidation to dehydro-L-ascorbic acid (L-// fi (9-2,3-hexodiulosonic acid y-lactone) (3) (Fig. 1). Vitamin C is a redox system containing at least three substances L-ascorbic acid, monodehydro-L-ascorbic acid, and dehydro-L-ascorbic acid. Dehydro-L-ascorbic acid and the intermediate product of the oxidation, the monodehydro-L-ascorbic acid free radical (2), have antiscorbutic activity equal to L-ascorbic acid. 

The reversible oxidation of L-ascorbic acid to dehydro-L-ascorbic acid is the basis for its known physiological activities, stabiUties, and technical apphcations (2). The importance of vitamin C in nutrition and the maintenance of good health is well documented. Over 22,000 references relating only to L-ascorbic acid have appeared since 1966. 

This synthesis was the first step toward industrial vitamin production, which began in 1936. The synthetic product was shown to have the same biological activity as the natural substance. It is reversibly oxidized in the body to dehydro-L-ascorbic acid (3) (L-// fi (9-2,3-hexodiulosonic acid y-lactone), a potent antiscorbutic agent with hiU vitamin activity. In 1937, Haworth and Szent-Gyn rgyi received the Nobel Prize for their work on vitamin C. 

Chemical Properties. The most significant chemical property of L-ascorbic acid is its reversible oxidation to dehydro-L-ascorbic acid. Dehydro-L-ascorbic acid has been prepared by uv irradiation and by oxidation with air and charcoal, halogens, ferric chloride, hydrogen peroxide, 2,6-dichlorophenolindophenol, neutral potassium permanganate, selenium oxide, and many other compounds. Dehydro-L-ascorbic acid has been reduced to L-ascorbic acid by hydrogen iodide, hydrogen sulfide, 1,4-dithiothreitol (l,4-dimercapto-2,3-butanediol), and the like (33). 

---