2 0-Dehydro-16,17-dihydro-

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. 

Systematic names of the Hantzsch-Widman type, as well as fusion names, imply unsaturation to the extent of the maximum number of noncumulative double bonds. Suitable suffixes (Table 3) serve to identify the fully saturated derivatives. Partially unsaturated rings may be designated by hydro prefixes with locants and an even-numbered multiplier, such as 2,3-dihydro , applied to a fully unsaturated name, or by dehydro prefixes applied to the saturated name, e.g. (116). 

Reaction of thienopyrimidinediamines 45 with formaldehyde in the presence of hydrochloric acid gives 3,4-dihydro-57f-l-thia-3,5,6,8-tetraazaacenaiAthalenes 46. The use of triethyl orthoformate gives the 3,4-dehydro products <95LA1703 96KGS103 96CA(125) 167905 >. 

Introduction of a hydroxyl group into the protoberberine skeleton was successfully carried out by the hydroboration-oxidation method. Dihydro-berberine (90) was converted to ( )-epiophiocarpine (91) as a major product along with ( )-ophiocarpine (92) (Scheme 22) (71). 5-Hydroxyprotober-berines 94 and 95 were obtained from the 5,6-dehydro compound 93 (50) synthesized from papaverine via 54 (72). 

It would be interesting to learn whether 4,5-dihydro-5 a-hydroxy-4 a-methoxy-6a,12a-dehydro-a-toxicarol interferes with the enzymatic activity of topoisomerase. Note that taxol, a successful chemotherapeutic agent that hampers the normal microtubule machinery, has been suggested to involve additional cytotoxic pathways including p53-independent apoptosis of tumor cells and inhibition of topoisomerase II (42). 

Although hydrogenation of pyrrole over a rhodium/alumina catalyst gives some 1-pyrroline (Scheme 6.18a), a better method is to dehydro-halogenate A-chloropyrrolidine by heating it with alcoholic potassium hydroxide (Scheme 6.18b). 2,5-Dihydro-1//-pyrrole, containing 15% pyrrolidine, is obtained by the zinc/hydrochloric acid reduction of pyrrole. 

Atractyligenin-2-O-P-D-glucoside Sd 220 A083 Avenasterol, 5-dehydro Sd Ai07 Benzaldehyde, 3-4-dihydroxy Sd Ai22 Benzaldehyde Sd Hu aosz Benzofuran, 2-3-dihydro Sd Hu aosz... 

Alkyl-3-oxo-2,3-dihydro-<(benzimidazolo[l,2-d]-l,2,4-thiadiazol> eliminieren beim Erhitzen auf 160" Alkyl-isocyanat und Schwefel. Als Zwischenprodukt wird ein 1,2-Dehydro-benz-imidazol formuliert. Ohne Zusatz von Nukleophilen trimerisiert es zu Tribenzimidazo[l,2-a 1, 2 -c /",2"-e]triazin (Schmp. 380°) anwesende Phenole addieren sich zu 2-Ary loxy-benz-imidazolen653 z.B. ... 

Die Oxidation von 1-Amino-5,6-dimethy]-l,5-dihydro- mit Blei (IV)-acetat fiihrt unter Abspaltung von Stickstoff zu l, 2-DimethyI-5,6-dehydro-benzimidazol, das mit verschiedenen Dienen abgefangen werden kann655 z.B. ... 

Benzofuranic acids iraws-meranzinic acid (56).162 Euparinoid benzofurans the important class of euparinoids (extracts of plants of the Compositae family), contains benzofurans, dihydro-benzofurans, and also includes compounds with a hydronaphthofuran ring. We mention euparin (the earliest known) (5-acetyl-6-hydroxy-2-isopropenylbenzofuran) (57, R6=OH, R =H) 163 166, dehydro-tremetone (5-acetyl-2-isopropenylbenzofuran) (57, R6—R —H),167,168... 

Dihydro-1,3-benzoxazines (196) are formed by the reaction of phenols with a mixture of formaldehyde and primary aromatic amines in the molar ratio 2 1. Presumably the phenol first reacts with the appropriate iminium species to form an intermediate amine (195), which is then cyclized in a Pictet-Spengler type reaction (Scheme 81) (44JA1875). If 2-hydroxybenzylamines are employed then methylene derivatives are obtained, and if the formaldehyde is replaced by a-dicarbonyl compounds dehydro dimers (197) are produced (Scheme 82) <70BCJ226>. 

Based on 13C-NMR analyses, it has been assumed [62] that 6-methoxymellein, a polyketide compound, is synthesized by head-to-tail condensation of one acetyl-CoA and four malonyl-CoA to form 3,4-dehydro-6-hydroxymellein as an intermediate. This isocoumarin derivative is then reduced to its dihydro-form, 6-hydroxymellein, which then accepts a methyl-unit via Omethyltransferase. We have shown [63] that cell extracts prepared from elicitor-treated carrot root disks catalyzes... 

Solv. Cholesteryl Cholesteryl 7-Dehydro- Ergosterol Lanosterol Dihydro-... 

Solv. Ref. C- Cholesteryl acetate Dioxane/CHCl3 [65 a] Cholesteryl methyl ether Dioxane/CHCl3 [65 a] 7-Dehydro- cholesteryl acetate Dioxane/CHCl3 [65 a] Ergostcrol Dioxane/CHCl3 [65 a] Lanosterol CDC13 [587] Dihydro- lanosterol CDC13 [587]... 

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