Anions tributyltin hydride

Radical Diels-Alder reactions have been used mainly to synthesize polycyclic molecules. These reactions, like those that involve cations and anions as components, proceed quickly but generally do not give high yields. Thus, the tricyclic enone 14 is the result of an intramolecular Diels-Alder reaction of quenched vinyl radical intermediate 13 obtained by treating the iododienynone 12 with n-tributyltin hydride/2,2 -azobisisobutyronitrile (AIBN) [28] (Equation 1.11). 

Dowd and coworkers have ingeniously ring-expanded twelve-, fourteen- and fifteen-membered cyclic / -ketoesters using the following sequence. Reaction of the anion of the / -ketoester with diiodomethane followed by treatment with tributyltin hydride with AIBN, in benzene under reflux, gives a one-carbon ring expansion (equation 137)810. 

Highly selective reduction of aldehydes rather than ketones, even 4-f-butylcyclohexanone, has been achieved by a binuclear hydrido molybdenum anion (Et4N[ JL-HMo2(CO)io]) and acetic acid in refluxing THF," The stable complex is readily prepared from molybdenum hexacarbonyl, which can be recovered after reduction. The full value of this reagent in synthesis remains to be established. Tributyltin hydride has been shown to be effective for the selective reduction of aldehydes in the presence of dried silica gel which acts as a mild acid catalyst," The reaction proceeded at room temperature in cyclohexane, many common functional groups were inert under these conditions. 

The action of n-butyllithium in THF at low temperature leads to the anion. After reaction with an electrophilic compound, e hydrolysis can generally be carried out in polar solvents (acetone, alcohols, acetonitrile) in the presence of mercury(II) chloride or oxide and water.In other cases, NBS, - chloramine T, cerium(IV) ammonium nitrate, n-tributyltin hydride, trialkyloxonium tetrafluorobor-ate, thallium nitrate or photochemistry can be used. Desulfurization by Raney nickel gives hydro-carbons. ... 

Treatment of tributyltin hydride with a Grignard reagent enables preparation of the corresponding organotin anion, which undergoes the Cannizarro reaction with pentanal providing an acyl stannane (Scheme 12.130) [233]. 

Indolyl radicals can be generated under standard conditions by reacting 2-bromoindole with tributyltin hydride. 3-Methyl-1-tosylindole can be cyanated at C-2 in good yield by a mixture of TMSCN and PIFA via oxidation of the indole to a cation radical, then addition of cyanide anion. ... 

Another interesting use of TEMPO has been in free-radical substitution of alkyl halides. In this reaction, halides react with tributyltin hydride and TEMPO to yield A-alkoxyamine substitution products [18. This reaction is especially attractive in cases where anionic nucleophiles are sterically prevented from carrying out substitution reactions. An example of this can be seen in Barrett s synthesis of sucrose [18b], in which a stereoselective iodoetherification reaction was used to produce neopentyl alkyl iodide 13 (Scheme 5). Free radical substitution mediated by tributyltin hydride and TEMPO yielded A-alkoxyamine 14. The mechanism [19] involves TEMPO abstraction of hydrogen from tributyltin hydride [20] the stannyl radical then abstracts iodide from the substrate, and a second equivalent of TEMPO traps the resulting carbon radical. 

A delocalized 0-stannyl radical anion can also be generated from the reaction of an a,/ -unsaturated ketone or aldehyde with tributyltin hydride and radical initiator AIBN [3, 4, 5a, 5b]. Thus, a,/ -unsaturated carbonyl compound 4 (R or R = H or alkyl), can be reacted with wBu SnH under standard free-radical conditions to give allylic O-stannyl ketyl species (5 6), shown in Scheme 2. After hydrogen atom transfer to the -position of 6, a synthetically useful tin(IV) enolate is produced [5b, 5d, 5g. Allylic 0-stannyl ketyls have both one- (radical) and two-electron (anionic) sites for reactivity. These reactions can proceed in a sequential manner - a rapidly-evolving methodology in organic synthesis [2, 5, 8j. If the one-electron reactivity in 6 is used with a radicophile, then the tin enolate or two-electron reactivity can be used in reactions with suitable electrophiles (E ). Note that the carbonyl species. 

It was shown that a variety of readily available (Z) and ( )-enol phosphates are good stereoselective synthons. Thus as5unmetric epoxidation of these phosphates using Jacobsen s (Salen)Mn(ii) complex afforded a-hydroxy ketones in enantio-selectivity up to 96%. The reaction of enantiomerically enriched 2-methyl-2-nitro-3-(diphenylphosphatoxy)alkyl radicals (80) with tributyltin hydride and AIBN in benzene results in the formation of alkene radical/anion pairs (81) which are trapped intramolecularly, leading to pyrolidine and piperidine systems (82) with memory of stereochemistry (Scheme 17). ... 

Sodium borohydride adsorbed on alumina is a new reagent combination for the reduction of aldehydes and ketones to alcohols in aprotic solvents such as ether. Cyanoborohydride anion, [BHsCN] , supported on an anion-exchange resin containing quaternary ammonium groups has been found in preliminary results to be a successful and convenient reagent for, inter alia, the reduction of enones to allylic alcohols. Ease of work-up and retention of cyanide by the resin are obvious advantages. Carbonyl compounds can also be reduced to alcohols by tributyltin hydride in a cyclohexane-silica gel slurry aldehydes are selectively reduced in the presence of ketones and products are obtained by simple elution from the silica. Adsorption, and consequent polarization, of the carbonyl group by the silica seems to be important in the mechanism of this mild, non-basic, process. 

The seemingly complex imidazolone (78-3) is in fact obtained in a single step by reaction of the amino-ester (78-1) with the iminoether (78-2) derived from capro-nitrile. The relatively acidic proton on the heterocyclic ring is next removed by reaction with sodium hydride. This anion is then alkylated with the same biphenyl-methyl bromide (77-2) that was used to prepare losartan to afford (78-4). The nitrile group is in this case converted to the tetrazole by means of tributyltin azide, a reagent that involves milder conditions than the traditional acidic medium used to generate hydrazoic acid. Thus, treatment of (78-4) with the tin reagent affords irbesartan (75-5) [82]. 

O-Stannyl ketyls have been proposed as intermediates for almost 30 years. Much of the early work came from the laboratories of Davies [9a], Pereyre [3, 9b, 9c] and Beckwith [6a, 10] and provided a framework for a modern understanding of O-stannyl ketyls. These seminal studies were often focussed on mechanistic aspects of tin ketyls in a-cyclopropyl- and a-epoxy-ketone ring openings. In one of the first carbonyl-alkene cyclizations, it was determined that the tributyltin radical added to a ketone in a somewhat sluggish manner and that excess amounts of tin hydride were needed to drive the reaction to completion [6a]. It was also understood that a ketyl radical anion is more stable than a simple carbon-centered radical, likely attributed to more effective delocalization. Ketyl reactive intermediates are now being utilized in new strained-ring cleavage-recyclization sequences (see below) and are... 

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