Cleavage, reductive

R-C-R R-C-R R-C-C-R R-C RaC = CR R.UC-CHRj R-COH RCH3 R-COOH > RCHn Ra-C=0 > R.-CH, R-OH > R-H Cleavage Cleavage Reduction Reduction Reduction Reduction Reduction Irreversible Irreversible Irreversible Irreversible Irreversible Irreversible Irreversible... 

In an elegant synthetic application of iron-diene complexes, Knox30 has reported acylation of a series of 1-alkyl-substituted diene complexes which after cleavage, reduction and esterification give a series of moth pheromones (Scheme 11). 

To facilitate sequencing analysis and enzymatic cleavage, reduction and alkylation of the peptides to open their potential disulfide bridges is recommended. Several alkyl groups can be used acrylamide, iodoacetamide, and 4-vinylpyridine (4-VP). S-pyridylethylation is preferred over the other alkyl groups when Edman degradation (PTH-4-pyridylethylated-Cys is commercially available) and MS (addition of 57 Da per alkylated cysteine residue) have to be performed. 

Mercaptans from Ethylene Thioketal Cleavage/Reduction... 

Reduction of Si—Cl bonds in polysilanes is without extensive Si—Si bond cleavage. Reduction of Si Clj +j (n = 2-5) halides occurs, although SijCljj reduction even at — 1(X)°C is accompanied by some bond cleavage. High yields of cyclosilanes (n = 5) ... 

A carbonylation reaction with Ni(CO)4 generating 1,4,7-tricarbonyl compounds has also been published Synthesis of 1,6-dicarbonyl systems via mercury(II) intermediates and radical chain additions to electrophilic olefins has been achieved (equation 70). This sequence constitutes an umpolung if one considers that the carbonyl moiety is masked in siloxycyclopropanes TTireo-juvabione has been synthesized from a methoxycyclo-propane via a mercury(II) salt cleavage/reduction sequence ... 

Carbon-carbon bond formation by reductive elimination from Ni, Pd, or Pt complexes is widespread. In many cases it is presumed to occur as the final step in a catalytic cycle, whereby the organic product is expelled from the metal center, but in others it is a well-defined, mechanistically studied reaction. Elimination takes place from Ni, Pd, and Pt complexes in their - - 2 or + A oxidation states, and it may be promoted by thermolysis, by photolysis, or by nucleophilic attack at the metal center. The reaction may proceed by heterolytic or homolytic metal-carbon bond cleavage, reductive elimination, or dinuclear elimination, and more than one mechanism may operate. 

Piperidine Synthesis Oxidative Cleavage/Reductive Amination.31... 

The oxidative cleavage/reductive amination sequence was readily scaled. After standard aqueous workup, the final manipulation involved a simple filtration through silica gel to remove salts, polar by-products, and residual osmium from 5. The success of this procedure stems from the remarkable nonpolar nature of the tertiary amine. In the favored chair conformation, the 3,5-bicyclic aryl group shields the axial nitrogen lone pair and ensures an equatorial disposition of the benzyl group (Figure... 

Thus, the aldol shown, which is susceptible to Sharpless-type epoxidation, has been obtained from phytal and the protected hydroquinone (ref. 120). Formation of the epoxide presumably with a chiral peracid (or perhaps with a conventional peracid relying on the asymmetry of the substrate) and then cleavage reductively in t-butyl methyl ketone containing lithium aluminium hydride led to a diol. The benzylic hydroxyl group of this was hydrogenolysed to afford the hydroquinone dimethyl ether in 85% yield. Ceric ammonium nitrate (CAN) oxidation afforded the intermediate benzoquinone hydrogenation of which was reported to result in 2R,4 R,8 R-a-tocopherol by, presumably, avoidance of a racemisation step. 

Althought this decomposition mechanism is not yet well-defined (homolytic cleavage, reductive dimerization. hydride formation, or other mechanisms), it is practically meaningful. Styrene polymerization by CpTiMea/FAB carried out in the low-temperature regime (below the decomposition temperature) produces only atactic polystyrene, possibly via a car-bocationic polyaddition. However, at higher polymerization temperatures (above the decomposition temperature), highly syndiotactic polystyrene can be obtained by coordinative 2,1-polyinsertion. ... 

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