Stannanes, oxidation

Development of this approach to a synthetically useful level was reported by Still, who employed large excesses of the CrOs-pyridine oxidant. The trimethylstannyl group was introduced either by bromide displacement or conjugate addition to enones (using MesSnLi) to provide a range of secondary or tertiary stannanes. Oxidation with Cr03-2py (py pyridine) led to ketones, ketols or alcohols depending on the system (Scheme 1). 

In the case of tertiary stannanes, oxidation leads to mixtures of alcohols and alkenes and some allylic oxidation, although 1-adamantyltrimethylstannane, incapable of elimination, provided the tertiary alcohol in good yield (Scheme 2). 

SYNS BIOMET TBTO BIS-(TRI-N-BUTYLCIN)OXID (CZECH) BISCTRIBLTYLOXIDE) of TIN BIS(TRIBUTYLSTANNYL)OXIDE BIS(TRI-N-BUTYLZINN)-OXYD (GERMAN) BTO BUTINOX C-Sn-9 ENT 24,979 HEXABUTYLDISTANNOXANE HEXABUTYLDITIN KYSLICNIK TRI-N-BUTYLCINICITY (CZECH) LS. 3394 OTBE (FRENCH) OXYBIS(TRIBUTYLTIN) OXYDE de TRIBUTYLETAIN TBOT O TBTO TRI-n-BUTYL-STANNANE OXIDE TRIBUTYLTIN OXIDE... 

CAS 56-35-9 EINECS/ELINCS 200-268-0 Synonyms Bis (tributylstannyl) oxide Bis(tributyltin) oxide Bis (tri-n-butyltin) oxide BTO HBD Hexabutyidistannoxane Oxybis (tributyltin) TBT TBTO Tri-n-butyl-stannane oxide... 

Hexabutyidistannoxane Oxybis (tributyltin) TBT TBTO Tri-n-butyl-stannane oxide... 

Lithiation at C2 can also be the starting point for 2-arylatioii or vinylation. The lithiated indoles can be converted to stannanes or zinc reagents which can undergo Pd-catalysed coupling with aryl, vinyl, benzyl and allyl halides or sulfonates. The mechanism of the coupling reaction involves formation of a disubstituted palladium intermediate by a combination of ligand exchange and oxidative addition. Phosphine catalysts and salts are often important reaction components. 

Selenium oxide (SeO,) [7446-08-4], 25 Silane, tnchloro [ 10025-78-2], 83 Sodium azide [26628-22-8], 109 Sodium hydride [7646-69-7], 20 Stannane, tetrachloro- [7646-78-8], 97 Sulfuric acid, diethyl ester [64-67-5], 48 dimethyl ester [77-78-1], 62 Sulfuryl chloride isocyanate [1189-71-5], 41... 

Allyl carbamates also can serve as amino-protecting groups. The allyloxy group is removed by Pd-catalyzed reduction or nucleophilic substitution. These reactions involve formation of the carbamic acid by oxidative addition to the palladium. The allyl-palladium species is reductively cleaved by stannanes,221 phenylsilane,222 formic acid,223 and NaBH4,224 which convert the allyl group to propene. Reagents... 

A third route to nonracemic a-alkoxy and a-hydroxy stannaries employs the chiral acetal 73 prepared from (f ,f )-2,4-pentanediol (Scheme 30)66. Addition of various Grignard reagents to this acetal in the presence of TiCLt results in selective displacement yielding (S )-a-alkoxy stannanes. The corresponding a-hydroxy derivatives can be obtained after oxidation and mild base treatment. Organocuprates can also be employed to cleave this acetal but with somewhat lower selectivity67. 

Cyclic stannanes can be generated by reaction of stannylenes with alkynes112. For example, bis[bis(trimethylsilyl)methyl]tin reacts with cyclooctyne to provide A1,18-9,10-(distanna-9,9,10,10-tetrakis[bis(trimethylsilyl)methyl])bicyclo[6,2,0]-decene, 69. This reaction is a typical oxidative addition on stannylenes. 

The Stille reaction of 2-chloro-3,6-diisopropylpyrazine (7) and 2-chloro-3,6-diisopropylpyrazine 4-oxide (9) with tetra(p-methoxyphenyl)stannane (readily prepared in situ from the corresponding Grignard reagent and SnCU) led to the corresponding arylation products 8 and 10, respectively [9]. Additional Stille coupling reactions of chloropyrazines and their N-oxides have been carried out with tetraphenyltin [10] and aryl-, heteroaryl-, allyl- and alkylstannanes [11]. 

Homolytic hydrostannation can also be initiated at room temperature by thiophenols, when a trace of oxygen may oxidize the thiol to the ArS radical, which abstracts hydrogen from the stannane to give the stannyl radical (Equation (15)).93 With azoisobutyronitrile (AIBN) initiation, alkynes undergo only monohydrostannation, but with the thiol, simple alkynes show bis(hydrostannation) or bis(stannation). 

Ge3H8) less flammable than silanes, are rapidly oxidized in air. Stannane (SnH4) decomposes rapidly even at 0°C plumbane (PbH4) has a doubtful existence. 

Anodic oxidation of a mixture of ds-cyclohexane-l,2-diol and cyclohexanol in methanol containing dibutyltin oxide and Et4NBr provides 2-hydroxycyclohexanone selectively, while cyclohexanol is recovered almost completely (Fig. 28) [146]. The cyclic intermediate dibutyl-(l,2-dioxycyclo-hexyl) stannan is oxidized indirectly by Br+. 

The [2 + 3] cycloaddition reaction of nitrile oxides, easily accessible from corresponding aldoximes, with different alkenes is known as an excellent route to isoxazohne derivatives . The reactions of asymmetric addition ° or addition of unsaturated ger-manes and stannanes to nitrile oxides were reviewed in recent years. In this subsection only the main directions of the synthesis of isoxazole derivatives are briefly reported. 

Crich and Rumthao reported a new synthesis of carbazomycin B using a benzeneselenol-catalyzed, stannane-mediated addition of an aryl radical to the functionalized iodocarbamate 835, followed by cyclization and dehydrogenative aromatization (622). The iodocarbamate 835 required for the key radical reaction was obtained from the nitrophenol 784 (609) (see Scheme 5.85). lodination of 784, followed by acetylation, afforded 3,4-dimethyl-6-iodo-2-methoxy-5-nitrophenyl acetate 834. Reduction of 834 with iron and ferric chloride in acetic acid, followed by reaction with methyl chloroformate, led to the iodocarbamate 835. Reaction of 835 and diphenyl diselenide in refluxing benzene with tributyltin hydride and azobisisobutyronitrile (AIBN) gave the adduct 836 in 40% yield, along with 8% of the recovered substrate and 12% of the deiodinated carbamate 837. Treatment of 836 with phenylselenenyl bromide in dichloromethane afforded the phenylselenenyltetrahydrocarbazole 838. Oxidative... 

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