Tin reagents

For other reactions of allylic stannanes, look under the functional group introduced see also page 386, Section 21. 

E+ =RX, RCHO, R2CO, CICO2R, Me3SiCl, R3SnCl, RSSR 

Phs O-a-BujSnOTf RCH(02CR)SePh, AIBN R2C(SMe)2, (Me2SSMe)BF4 (R=CR2SMe) RCH=NR, Lewis acid 

RCONRCOCHIR ROjCCHBrNRCOR ROjCCHBrNHCOR NOzCRFCOjR (R = CRFC02R) N02CR2F (R=CR2F) 

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Acetylsucrose [63648-81-7] has been prepared in 40% yield by direct acetylation of sucrose using acetic anhydride in pyridine at 40° C (36). The 6-ester has subsequently been obtained in greater than 90% yield, by way of 4,6-cycHc orthoacetate. Other selective methods for the 6-acylated derivatives include the use of alkyl tin reagents such as dibutyl tin oxide (37) and of dibutyl stannolane derivatives (38). Selective acetylation of sucrose by an enzymic process has also been described. Treatment of sucrose with isopropenyl acetate in pyridine in the presence of Lipase P Amano gave, after chromatography, 6-0-acetylsucrose (33%) and 4/6-di-O-acetylsucrose (8%). The latter compound has been obtained in 47% yield by the prolonged treatment (39). 

Primary and secondary alkyl haUdes react well, but alkyl haUdes ate preferentially dehydrohalogenated by the tin reagents. 

The iodide ion induced decomposition of trimethyl (trifluoromethyl) tin and of phenyl (trifluoromethyl) mercury represent additional interesting possibilities. The reaction of the tin reagent and iodide ion with (31, X = H) in refluxing glyme for 168 hr gives (32) and the corresponding 6jff,7j0-difluoromethylene adducts in 46% and 7% yields, respectively. ... 

On the other hand, the corresponding tin precursor (63) undergoes smooth cycloaddition with a wide variety of aldehydes to produce the desired methylene-tetrahydrofnran in good yields [32, 33]. Thus prenylaldehyde reacts with (63) to give cleanly the cycloadduct (64), whereas the reaction with the silyl precursor (1) yields only decomposition products (Scheme 2.20) [31]. This smooth cycloaddition is attributed to the improved reactivity of the stannyl ether (65) towards the 7t-allyl ligand. Although the reactions of (63) with aldehydes are quite robust, the use of a tin reagent as precursor for TMM presents drawbacks such as cost, stability, toxicity, and difficult purification of products. 

The Lewis acid mediated addition of allylic tin reagents to nitroalkenes has been reported. The condensation reaction of tributyl[(Z)-2-butenyl]tin(IV) with (E)-(2-nitroethenyl)benzene or (L)-l-nitropropene catalyzed by titanium(IV) chloride proceeded with modest anti diastereoselectivity. Poorer diastereoselection resulted when diethyl ether aluminum trichloride complex was employed as the Lewis acid 18. 

Tin reagents such as Sn[N(TMS)2]2 in the presence of an amine can also be use to convert an ester to an amide. This reagent can also be used to convert p-amino esters to P-lactams. The ester-to-amide conversion has also been accomplished electrochemically, by passing electric current in the cathodic compartment. 

In a related reaction, aryl halides couple with vinyl tin reagents to form styrene derivatives in the presence of a nickel catalyst, for example, ... 

Nucleophilic addition reactions of allylic tin reagents to chiral 3-substituted 3,4-dihydroisoquinolines 89 activated by acyl chlorides afford trans 1,3-disubstituted 1,2,3,4-tetrahydroisoquinolines 90 stereoselectively <95CL1003>. 

The Stille coupling reaction is very versatile with respect to the functionality that can be carried in both the halide and the tin reagent. Groups such as ester, nitrile, nitro, cyano, and formyl can be present, which permits applications involving masked functionality. For example, when the coupling reaction is applied to l-alkoxy-2-butenylstannanes, the double-bond shift leads to a vinyl ether that can be hydrolyzed to an aldehyde. 

Stoichiometric use of a tin reagent to prepare the phenylacetone 4 Toxicity of tin compounds, and operational inefficiency based on high molecular weight of reagent and excessive chromatography required to reject tin residues... 

Allylations, allenylations, and propargylations of carbonyl compounds in aqueous media can also be carried out with preformed organic tin reagent, rather than the use of metals.86,87,88 For example, the allylation reaction of a wide variety of carbonyl compounds with tetraal-lyltin was successfully carried out in aqueous media by using scandium trifluoromethanesulfonate (scandium triflate) as a catalyst (Eq. 8.40).89 A phase-transfer catalyst (PTC) was found to help the allylation mediated by tin at room temperature without any other assistance.90... 

Due to the toxicity of tin reagents, a new radical elimination without using Bu3SnH is highly desirable. B arton has reported that nitro olefins are converted into olefins via radical elimination of P-nitro trithiocarbonates (Eq. 7.116).160 The Michael addition of trithiocarbonate to nitroalke-nes is carried out in CS2 to avoid the addition of EtSH. 

The tin can now be displaced by butyllithium to give a carbanion and a new group attached Scheme 44 shows the nub of a synthesis of dendrolasin (88) which illustrates the use of the tin reagent to avoid the 2-alkylation that would otherwise occur224 (cf. Scheme 41). 

Scheme 7.77 Radical cydizations using fluorous tin reagents.

Among the many applications of fluorous chemistry is the Stille coupling of tin reagents with fluorinated tags in which the products and excess of the tin-containing reagents can be conveniently removed from the reaction mixture, and recycled. Un-... 

Other tin reagents have found use in Pd-catalyzed cross-couplings with halopyridines as well. The Stille coupling of 3-iodopyridine with ethoxy(tributylstannyl)acetylene gave rise to 3-ethoxyethynylpyridine (100), which was then hydrolyzed to the corresponding ethyl 3-pyridylacetate (101) [88], Carbamoylstannane 102 was prepared by sequential treatment of lithiated piperidine with carbon monoxide and trimethyltin chloride. Stille coupling of carbamoylstannane 102 and 3-bromopyridine provided a unique entry to amide 103 [89],... 

Benzotrifluoride dissolves both organic substrates/products and fluorous tin reagent... 

D. P. Curran, Z. Luo, P. Degenkolb, Propylene Spaced Allyl Tin Reagents A New Class of Fluorous Tin Reagents for Allylations under Radical and Metal-Catalyzed Conditions , Bioorg. Med Chem. Lett. 1998, 8,2403. 

We usually conduct solid phase extractions on small scale and have not focused on the recovery of the tin reagents. However, in principle this should be possible for many types of reactions. 

Organogermanium compounds can be prepared by transmetallation reactions with tin reagents. Examples include Me2PhGeCl (Equation (66)),89 the alkene-functionalized species 26-28, (Equations (67) and (68)),90 and the allenic (Equation (69)) and propargylic (Equation (70)) species 29 and 30.91 A series of aryltrichlorogermanes was prepared from the corresponding tin reagents (Equation (71), Table 9).92 Transmetallation with zirconium species can also be used (Equation (72), Table 10).93... 

There can be two kinds of chiral tin reagents tin chiral and C-chiral. Early reports of chiral tin hydride involved transfer of chirality via a chiral tin center [45-47]. These tin hydrides were prone to racemization. Thus, chiral carbon-based ligands attached to the tin center were synthesized to minimize racemization. The first chiral tin hydride containing a C2-symmetric binaphthyl substituent was reported by Nanni and Curran (Scheme 16) [48]. a-Bromoketone 58 was reduced by chiral tin hydride 59 (R3 = Me), where the reactivity and selectivity was dependent on the reaction conditions (entry 4). 

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