Tributyltin hydride compounds

Quebrachitol was converted into iL-c/j/roinositol (105). Exhaustive O-isopropylidenation of 105 with 2,2-dimethoxypropane, selective removal of the 3,4-0-protective group, and preferential 3-0-benzylation gave compound 106. Oxidation of 106 with dimethyl sulfoxide-oxalyl chloride provided the inosose 107. Wittig reaction of 107 with methyl(triphenyl)phos-phonium bromide and butyllithium, and subsequent hydroboration and oxidation furnished compound 108. A series of reactions, namely, protection of the primary hydroxyl group, 0-debenzylation, formation of A-methyl dithiocarbonate, deoxygenation with tributyltin hydride, and removal of the protective groups, converted 108 into 7. 

Radical cyclization of the indole thioesters 107 and 110 with tributyltin hydride and 2,2 -azobisisobutyronitrile (AIBN) gives a mixture of products in each case the 6-< Wo-cyclization product (the indolonaphthyridine, 109 or 112) and the 5-f vv-cyclisation product (the spiro compound 108 or 111) are obtained in approximately equal yield (Equations 22 and 23) <20040L759>. 

The triply benzo-fused pyrrolonaphthyridine 222 results by reduction of either 220 or 221 with tributyltin hydride and AIBN. This compound shows biological activity similar to 215 above, although interestingly 222 is more active in the protonated form (Equation 57) <2001J(P1)3180>. 

Reaction of an A-(o-halogcnobenzoyl)pyridoindole 360 with tributyltin hydride and azobis(cyclohexanecarbonitrile) gives the /vrr -fused pyrrolonaphthyridine 361 along with the (6 5 6) pyridoindolizine 362 (Equation 129). Compound 361 is obtained by the action of tributyltin hydride on the Ar-benzoyl-chloropyridoindolc 363 (Equation 130)... 

Tributyltin hydride reduction of carbonyl compounds. The reduction of carbonyl compounds with metal hydrides can also proceed via an electron-transfer activation in analogy to the metal hydride insertion into TCNE.188 Such a notion is further supported by the following observations (a) the reaction rates are enhanced by light as well as heat 189 (b) the rate of the reduction depends strongly on the reduction potentials of ketones. For example, trifluoroacetophenone ( re<1 = —1.38 V versus SCE) is quantitatively reduced by Bu3SnH in propionitrile within 5 min, whereas the reduction of cyclohexanone (Erea — 2.4 V versus SCE) to cyclohexanol (under identical... 

Intermediates such as 224 resulting from the nudeophilic addition of C,H-acidic compounds to allenyl ketones such as 222 do not only yield simple addition products such as 225 by proton transfer (Scheme 7.34) [259]. If the C,H-acidic compound contains at least one carbonyl group, a ring dosure is also possible to give pyran derivatives such as 226. The reaction of a similar allenyl ketone with dimethyl mal-onate, methyl acetoacetate or methyl cyanoacetate leads to a-pyrones by an analogous route however, the yields are low (20-32%) [260], The formation of oxaphos-pholenes 229 from ketones 227 and trivalent phosphorus compounds 228 can similarly be explained by nucleophilic attack at the central carbon atom of the allene followed by a second attack of the oxygen atom of the ketone at the phosphorus atom [261, 262], Treatment of the allenic ester 230 with copper(I) chloride and tributyltin hydride in N-methylpyrrolidone (NMP) affords the cephalosporin derivative 232 [263], The authors postulated a Michael addition of copper(I) hydride to the electron-... 

Allenyl ethers are useful key building blocks for the synthesis of a-methylene-y-butyrolactones [129, 130], The synthesis of the antileukemic botryodiplodin was accomplished with the crucial steps briefly presented in Scheme 8.56. Bromoallenyl ethers 225 were easily prepared by base-induced isomerization from the corresponding /3-bromoalkyl alkynyl ether compounds and then subjected to electrophilic bro-mination with NBS. The resulting acetals 226 were converted into 2-alkoxy-3-methy-lenetetrahydrofurans 227 by dehydrohalogenation of the alkenyl bromide unit to an alkyne and subsequent radical cyclization employing tributyltin hydride [130],... 

The silylated tin compound 199, obtained from tributyltin hydride and N-bis(trimethylsilyl)propargylamine (198) in the presence of a trace of AIBN (2,2/-azobisisobutyronitrile), is a versatile reagent for the preparation of allylic amines. Treatment with aryl bromides ArBr (Ar = Ph, 4-MeOCgH4, 4-O2NC6H4 etc.) under Pd(PPh3)4 catalysis yields the silylated amines 200, which are hydrolysed by acids to the free amines 201. 199 is converted into the lithium compound 202, which is transformed into 203 by aqueous ammonium chloride and into 204 by the action of alkyl halides RX (R = Me, Et or allyl) (equation 76)204. 

The same research group has further performed radical carbonylation reactions on the same microreactor system [36]. First, alkyl halides were initiated and effectively reacted with pressurized carbon monoxide to form carbonyl compounds. The principle was subsequently successfully extrapolated to the multicomponent coupling reactions. 1-Iodooctane, carbon monoxide and methyl vinyl ketone were reacted in the presence of 2,2 -azobis(2,4-dimethylvaleronitrile) (V-65) as an initiator and tributyltin hydride or tris(trimethylsilyl)silane (TTMSS) as catalyst (Scheme 15). 

Barton-McCombie deoxygenation is not always stereoselective the diastereo-meric ratios strongly depends on the nature of the protecting groups and of the ester moiety. However, in 2-C-trifluoromethyl-2-deoxyfuranose, the a compound is the major product of the reaction, due to steric hindrance of this a side. In 3-C-trifluoromethyl-3-deoxyfuranose, deoxygenation by tributyltin hydride yields only the a product, if it is performed with oxalate instead of thiocarbonate. Another possibility to obtain this selectivity is to perform the reaction with 1,2,5,6-di-O-isopropylidene-a-D-glucofuranose (Figure 6.34). ... 

Our approach was to use the unsaturated bromodeoxylactones in an intramolecular radical reaction, since these compounds possess both the radical precursor and the radical trap within the same molecule. Thus, reacting the unsaturated bromodeoxyheptonolactone 20 (Scheme 14) with tributyltin hydride and a radical initiator, the bicyclic lactone 65 a was obtained in a quantitative yield within 1 h. The stereocontrol in the reaction was determined by the structure of the product, since the compound obtained has two fused cyclopentane rings which can only be cis anellated. The radical A, which is the intermediate, was trapped by the tin hydride. The stereochemistry of the newly formed chiral center is determined by the configuration at C-4 in the educt 20 [45]. 

Treatment of the tricyclic compound 133 with tributyltin hydride and 2,2 -azobisisobutyronitrile (AIBN) produces a radical which cyclizes to give 134 creating a new quaternary center (Equation 35) <2002JA2080>. 

Radical carbonylation reaction serves as a powerful tool for the synthesis of a range of carbonyl compounds. Radical carbonylation has been successfully applied to the synthesis of functionalized ketones from alkyl, aryl, and alkenyl halides.The radical aminocarbonylation reaction of alkynes and azaenynes provided efficient routes to 2-substituted acrylamides, lactams, and pyrrolidinones. For example, the aminocarbonylation of 4-pentyn-l-yl acetate 318 initiated by tributyltin hydride (Bu"3SnH) (30mol%) with AIBN (20mol%) gave acrylamide 325 in 92% yield (Scheme 43).A proposed mechanism starts from the addition of tributyltin radical 319 to alkyne... 

The compounds obtained by the replacement of ring sulfur by carbon, as in the case of penicillins, show somewhat improved antibiotic properties. A free radical— based route has been described for the conversion of fermentation derived cephalosporins to their carbocyclic derivatives. The first step in this sequence consists of the condensation of the cephalosporin sulfone (36-1) with formaldehyde and dimethyla-mine the initial product from the Mannich-like reaction consists of the exomethylene derivative at the position adjacent to the activating sulfone. The product is treated in situ with phenylselenol to give the Michael adduct (36-2). This fragments with an extmsion of sulfur dioxide when heated with the free radical initiator AIBN in the presence of tributyltin hydride the reaction can be envisaged as leading to the... 

Trimethylsilyl-protected 1-isopropenylcyclobutanols were rearranged to cyclohexanones via a two-step reaction sequence.114 The vinylcyclobutanes 1 were first treated with mercury(II) trifluoroacetate. The crude products were then converted into chlorides (which can be isolated) and finally reduced with tributyltin hydride to give 2. Sometimes small amounts of five-mem-bered ring compounds, which are intermediates of this two-step ring enlargement, are formed as side products. 

The facile formation of the iodo compound, and the subsequent reduction with tributyltin hydride opens a new access to 2-amino-2,3-dideoxy-D-glucose (D-lividosamine) present in various aminoglycoside antibiotics [92], The same strategy been used in the synthesis of C-lO -C-l fragment of boromycin [93]. Displacement of the C-3 imidazylate ester of a 2-azido-2-deoxy-a-D-altropyranose derivative with benzoate occurred readily [94], compared with the corresponding tosylate [95],... 

Radical chain chemistry is often employed for the transformation of an alcohol to the corresponding deoxy derivative. The secondary alcohol 1 is first converted into a suitable thiocarbonyl derivative. The first derivatives investigated were thioxobenzoates 2, xan-thates 3, and thiocarbonylimidazolides 4 (Scheme 2). On reduction with tributyltin hydride, these derivatives afforded a good yield of the appropriate deoxy compounds [8-10]. 

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