Potassium reductive dimerization

Symmetrical 3,5-dialkyl-l,2,4-trithiolanes (178) can be synthesized in reasonable yield by chlorination of dialkyl disulfides (175) to a-chiloroalkyl sulfenyl chlorides (176), which are then reacted with potassium iodide to give di-a-chloroalkyl disulfides (177). Subsequent cyclization with sodium sulfide gave (178) (72T3489). When (176) was treated with one molar equivalent of sodium sulfide, the reductive dimerization and cyclization was effected in one step (78HCA1404). Treatment of perfluoropropene with sodium hydrogen sulfide in THF resulted in the formation of 3,5-bis(2,2,2-trifluoroethyl)-l,2,4-trithiolane (179) (72IZV2517). 

Alkenes can be obtained from aldehydes or ketones on reductive dimerization by treatment with a reagent prepared from titanium(III) chloride and zinc-copper couple (or L1A1H4), or with a species of active titanium metal formed by reduction of titanium(III) chloride with potassium or lithium metal. This McMurry coupling reaction is of wide application, but in intermolecular reactions generally affords a mixture of the E- and Z-alkenes (2.99). 

Reductive dimerization of chalcones by ultrasonically dispersed potassium (UDP) is initiated by an electron transfer to the enone system. The reaction is not selective however, details are not easily available. ... 

The only other ambient stable low oxidation state magnesium compound to be reported outside our group is the dianionic magnesium(I) dimer, 14, which was prepared in one pot by the potassium reduction of the a-diimine,... 

Phosphoric acid/phosphorus potassium iodide Reductive dimerization of ketones... 

These reactions are usehil for the preparation of homogeneous difunctional initiators from a-methylstyrene in polar solvents such as tetrahydrofuran. Because of the low ceiling temperature of a-methylstyrene (T = 61° C) (26), dimers or tetramers can be formed depending on the alkaU metal system, temperature, and concentration. Thus the reduction of a-methylstyrene by sodium potassium alloy produces the dimeric dianionic initiators in THF (27), while the reduction with sodium metal forms the tetrameric dianions as the main products (28). The stmctures of the dimer and tetramer correspond to initial tail-to-tail addition to form the most stable dianion as shown in equations 6 and 7 (28). 

For enzymatic reductions with NAD(P)H-dependent enzymes, the electrochemical regeneration of NAD(P)H always has to be performed by indirect electrochemical methods. Direct electrochemical reduction, which requires high overpotentials, in all cases leads to varying amounts of enzymatically inactive NAD-dimers generated due to the one-electron transfer reaction. One rather complex attempt to circumvent this problem is the combination of the NAD+ reduction by electrogenerated and regenerated potassium amalgam with the electrochemical reoxidation of the enzymatically inactive species, mainly NAD dimers, back to NAD+ [51]. If one-electron... 

Stereospecific ketone reduction was also observed (Giordano et al. 1985) with potassium, rubidium, and cesium (but not with sodium) in tertiary alcohols (but not in secondary or primary alcohols). The undesirable dimerization probably proceeds more readily in the case of sodium. Tertiary alcohols are simply more acidic than primary or secondary alcohols. It is reasonable to point out that the ketone-to-alcohol reduction of 3a-hydroxy-7-oxo-5p-cholic acid by alkali metals is a key step in the industrial synthesis of 3a,7p-dihydroxy-5p-cholic acid. 

Reaction of 1 with excess 103 in toluene gives the mixed carbamate (104) in 21% yield after chromatography on silica gel. Reduction of the S—S bond present in this carbamate is accomplished with zinc dust in acetic acid to give the A(-(2 -mercaptoethyl) oxazolidinedione (105) in high yield. Dimerization of 105 is then achieved by reaction with excess aqueous potassium ferricyanide to give the disulfide (106). 

Pt(II) compound reactivation, 37 201 Pt(IV) compound reduction, 37 201 rate-determining step, 37 199-201 tetrachloride, 4 187-188 tetracyanide anions, as one-dimensional electrical conductors, 26 235-268 anion-deficient structures anhydrous compounds, 26 252-254 dimerization, 26 249-251 hydrated derivatives, 26 245-252 physics, 26 260-263 with potassium bromide, 26 248-249 with rubidium chloride, 26 249-250 cation-deficient compounds, 26 244, 254-256... 

Using a different dimerization method, namely phenolic oxidation, chiral substrates react in a more stereoselective manner than under reductive conditions. The choice of oxidizing reagent may drastically affect the stereochemical outcome of the reaction. Thus, when potassium hexacyanoferrate(III) is used (17 )-l,2,3,4-tetrahydro-6-methoxy-l,2-dimethyl-7-isoquino-linol couples to give a mixture of atropisomers 3 in 38 % yield and with a d.r. (M)I(P) of 45 553,4. Only one single atropisomer, namely (A/)-3, is formed, in a 66% yield by anodic oxidation, which is attributed to electrode surface effects3. 

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