Potassium reductions with

Kyba and eoworkers prepared the similar, but not identical compound, 26, using quite a different approach. In this synthesis, pentaphenylcyclopentaphosphine (22) is converted into benzotriphosphole (23) by reduction with potassium metal in THF, followed by treatment with o "t/20-dichlorobenzene. Lithium aluminum hydride reduction of 23 affords l,2-i>/s(phenylphosphino)benzene, 24. The secondary phosphine may be deprotonated with n-butyllithium and alkylated with 3-chlorobromopropane. The twoarmed bis-phosphine (25) which results may be treated with the dianion of 24 at high dilution to yield macrocycle 26. The overall yield of 26 is about 4%. The synthetic approach is illustrated in Eq. (6.16), below. 

The tosylhydrazone is prepared from the carbonyl compound and then reduced with lithium aluminium hydride, sodium borohydride or potassium borohydride. In this way D-glucose tosylhydrazone was converted into crystalline 1-deoxyglucitol by reduction with potassium borohydride... 

The metallocene dichloride of zirconium and hafnium 20b and 20c were also prepared and underwent reduction with potassium to give monomeric metallocene monochloride complexes 21b and 21c (Eq. 8) [39b]. The structure of the zirconocene complex 21 b in the crystal showed a conformation which suggests a less steric strain as compared to 21a due to zirconium s larger atomic size. As a consequence of the coordinative unsaturation an unusually short Zr —Cl bond length was found. 

For preparative purposes, titanium metal can be used in place of sodium or lithium in liquid ammonia for both the vinyl phosphate231 and aryl phosphate232 cleavages. The titanium metal is generated in situ from TiCl3 by reduction with potassium metal in tetrahydrofuran. 

Other selected examples include tris(tetramethylethylene diamine-sodium)-9,9-dianthryl 143,154 alkali metal salts of 9,10-bis(diisopropylsilyl)anthracene 144,155 as well as the closely related naked 9,10-bis(trimethylsilyl)anthra-cene radical anion 145.156 This chemistry is further extended to the solvent-shared and solvent-separated alkali metal salts of perylene radical anions and dianions 146, 147,156 while other examples focus on alkali metal salts of 1,2-diphenylbenzene and tetraphenylethylene derivatives, where reduction with potassium in diglyme afforded contact molecules with extensive 7r-bonding, [l,2-Ph2C6H4K(diglyme)] 148.157 Extensive 7r-coordination is also observed in (1,1,4,4 tetraphenylbutadiene-2,3-diyl)tetracesiumbis(diglyme)bis(methoxyethanolate) 149.158... 

Ethinyloestradiol (133), irradiated at 450 nm in a mixture of aqueous buffer (pH 7.4) and methanol 7 3 in the presence of oxygen and the photosensitizer hematoporphyrin, gave the peroxide (134), identified by its ready reduction with potassium iodide to the corresponding alcohol [95]. Oestrone (135) reacted similarly [96]. 

Earlier work on the determination of total mercury in river sediments also include that of Iskander et al. [41], Iskander applied flameless atomic absorption to a sulphuric acid nitric acid digest of the sample following reduction with potassium permanganate, potassium persulphate and stannous chloride. A detection limit of one part in 109 is claimed for this somewhat laborious method. 

At the outset of our studies of the reactivity of I and II, it was necessary to investigate claims that tertiary henzamides were inappropriate substrates for the Birch reduction. It had been reported that reduction of A,A-dimethylbenzamide with sodium in NH3 in the presence of tert-butyl alcohol gave benzaldehyde and a benzaldehyde-ammonia adduct. We formd that the competition between reduction of the amide group and the aromatic ring was strongly dependent on reaction variables, such as the alkali metal (type and quantity), the availability of a proton source more acidic than NH3, and reaction temperature. Reduction with potassium in NH3-THF solution at —78 °C in the presence of 1 equiv. of tert-butyl alcohol gave the cyclohexa-1,4-diene 2 in 92% isolated yield (Scheme 3). At the other extreme, reduction with lithium in NH3-THF at —33 °C in the absence of tert-butyl alcohol gave benzaldehyde and benzyl alcohol as major reaction products. ... 

The influence of pH on the reaction of 2,4,6-triphenylpyrylium salts is significant. In neutral conditions the sole product is the ring-opened enedione (26), but at high pH the 2-hydroxypyran (25 R = H) is formed (Table 1) (69TL2195). Reaction of this pyran with Grignard reagents affords an equimolar mixture of the substituted 2H- and 4//-pyrans (27) and (28), whilst 2,4,6-triphenyl-2//-pyran results on reduction with potassium borohydride. 

Normal human fibroblasts grown in media with 12% fetal calf serum were treated with or without galactose oxidase and then subjected to reduction with potassium borotritiide. GSLg were isolated and subjected to acid-catalyzed methanolysis (62) (see Materials and Methods). Methyl glycosides, methyl sphingosine, and fatty acid methyl esters were isolated by extraction of the total hydrolysate with solvents as described previously (62). Radioactivity was measured in triplicate in aliquots of these extracts. 

Fibroblasts grown in media with 12% fetal calf serum were treated with galactose oxidase, followed by reduction with potassium borotritiide. The individual GSLs were isolated and the radioactivity was measured in triplicate (see Materials and Methods). 

Various cross-conjugated enediynes undergo Bergman-type cycloaromatizations upon reduction with potassium metal, generating anions of fulvenes and fulvalene derivatives (Scheme l).6 Not all cross-conjugated enediynes yield cyclized dianions upon reduction some give uncyclized, Y-shaped, cross-conjugated dianions, whereas others apparently yield radical anions that either dimerize or persist as monomers. 

In order to introduce a second hydroxyl group al C-l 1 of the ester (99) its sodium salt was treated with p-nitrobenzene diazonium chloride in methanol. The resulting product on methylation and then reduction with potassium dithionate afforded the amino ester (100). Diazotization and methanolysis produced ethyl ( )-camosate dimethyl ether (101), which on saponification produced camosic acid dimethyl ether (102). Wenkert [22] accomplished demethylation of dextrorotatory camosic dimethyl ether with boron tribromide. Thus the work of Meyer lacks only the... 

On the basis of this structure, most of the reactions of apopseudoakuammigine can be satisfactorily explained. The reduction with potassium borohydride can be accounted for, as postulated by Joule and Smith, by the reverse Mannich decomposition of LXII, followed by reduction of the intermediate (LXIII) the product of this reaction would then be the indolic amino acid LXIV, a structure which is consistent with the observation that this amino acid is extremely resistant to esteri-... 

The new selenacrown ether A,A -dimethyl-l,ll-diaza-4,8,14,18-tetraselenacycloicosane 32 has been synthesized and characterized <2005MI191>. Xu et al. have reported the first selenacrown and selenazacrown ethers bearing a hydroxy group. In this series, the key step is the preparation of the diselenide intermediate 188 by a reduction with potassium borohydride. It can then be condensed with dihalides or diol ditosylates 191 to give the aza 10-membered... 

Potassium hyponitrite, K2N202.—The hyponitrite can be prepared from potassium nitrite by reduction with potassium-amalgam, or electro-lytically.6 Its heat of formation in aqueous solution is 116-2 Cal.7... 

---