Ring hydrogenation isocycles

Palladium-calcium carbonate/quinoline Hydrogenation of acetylene derivatives partial and selective s. 16, 80 Palladium-strontium carbonate Partial ring hydrogenation of isocyclics s. 17, 89... 

Sodium tetrahydridoboratelirradiationidicyanobenzene Partial ring hydrogenation of isocyclics... 

Selective ring hydrogenation of isocyclics s. 13, 74 Reductive furan ring opening s. U, 74... 

Ketones and alcohols from a,y -ethyleneketones s. 12, 96 Ring hydrogenation of isocyclics of benzene rings s. 12, 98 stereospecific s. 11, 104 partial s. 13, 94... 

Ring hydrogenation of isocyclic amines preferential s. 12, 106 Ring hydrogenation of steroids... 

The reactions in Methods A, B and C, which all start from pyrylium salts are analogous to the well-known conversions of 2.4.6-substituted pyrylium salts 27 with ammonia, primary amines, hydrogen sulfide or the anions of CH activated compounds to the corresponding heterocyclic or isocyclic aromatic systems The first step involves addition of the basic phosphine at C-2 (or C-6) to form 2S. Ring-opening, ring-closure and elimination of water are likely steps in the formation of the product 2. 

Chlorophyll a (L.P. Vernon, 1966) contains an unsymmetrical porphyrin chromophore with two special features the double bond between C-17 and C-18 is hydrogenated and carbon atoms 13 and 15 bear a carboxylated, "isocyclic cyclopentanone ring E. 

LithiumJliq. ammonia-sodium hydride Partial hydrogenation of isocycles with phenol ring retention... 

Hydrogen peroxide sodium hydroxide Oxidative cleavage of a,/ -ethyIeneketones Ring opening of isocycles... 

Nuclei s. Heterocyclics, Isocyclics, Rings Nucleophiles (s. a. G-Hydrogen, active)... 

N-nitrosourethans 17, 342 urethans 17, 342 Nitrous acid esters s. Alkyl nitrite Nitryl chloride 16,520 1 Nonanol as solvent 16, 728 Nuclei s. Heterocyclics, Isocyclics, Rings Nucleophiles (s. a. C-Hydrogen, active)... 

Hydrogen peroxide sulfuric acid Oxidative ring contraction of isocyclics Oxidative rearrangements of -diketones... 

Here the hydrogens are added to the /3-carbon atoms of the pyrrole rings (Figs. 1, 3). For example, chlorophyll is a dihydroporphyrin or chlorin (Figs. 1, 3) and has two main bands at 430 and 660 m/a. Bacterio-chlorophyll is a tetrahydroporphyrin or bacteriochlorin in this case the opposite pyrroles B and D are reduced (Fig. 3) here the two main bands are at 360 and 770 m/x. Attempts to prepare a hexahydro derivative have failed. A conjugated structure may be written for this compound but it would violate Huckels rule (17) for isocyclic carbon compounds, i.e., that [4n + 2]t electrons are needed for aromatic stability, where n is a positive integer. 

Hydrogen fluoride/antimony pentafluoride Reaction in superacidic medium Isocyclic ring closure with dearomatization of phenolethers... 

Hydrogen bromide/acetic acid Isocyclics from ketones Anthracene ring... 

Hydrogen peroxide/hydrogen chloride Oxidative ring contraction of isocyclics Benzene ring from tropenium salts... 

Chlorophyll, the pigment of green leaves, is a magnesium-contiuning porphyrin. The main features of the structure are the two supernumerary hydrogen atoms in ring IV, the isocyclic ring, and the phytyl side chain, which imparts lipid solu-... 

Sodium hydrogen carbonate Hydrolytic ring opening of isocycles... 

Startg. octalindione treated with 1 equivalent NaBH4 in ethanol to reduce the a,/ -satd. carbonyl, hydrogenated with Pd-on-charcoal in 3 1 ethyl acetate-triethylamine to eliminate the isocyclic double bond, the isoxazole ring hydro-genolyzed with Raney-Ni in ethanol, finally refluxed 7 hrs. with Og-free metha-nolic Na-methoxide then 15 hrs. with aq. 3%-NaOH -> tricyclic enone (startg. m. f. 837). Overall Y 60%. G. Stork and J. E. McMurry, Am. Soc. 89, 5461, 5459, 5463, 5464 (1967). 

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