Tin-mediated allylation

Otera et al. extended the tin-mediated allylation to 2-substituted allyl bromides.80 When 2-bromo and 2-acetoxy-3-bromo-l-propene were used, the allylation with tin produced the corresponding functionalized coupling products (Eqs. 8.36 and 8.37). In the case of 2,3-dibromopropene, the reaction occurred exclusively through allylation in the presence of the vinyl bromo group. The presence of other electrophiles such as a nitrile (-CN) or an ester (-COOR) did not interfere with the reaction. 

Luche found that tin-mediated allylations can also be performed through ultrasonic radiation, instead of using aluminum powder and hydrobromic acid to promote the reaction.82,83 The use of a saturated aqueous NH4C1/THF solution, instead of water/THF, dramatically increased the yield. When a mixture of aldehyde and ketone was subjected to the reaction, highly selective allylation of the aldehyde was achieved. 

Allylation of the C-3 position of the cephem nucleus was accomplished by either indium-mediated or indium trichloride-promoted tin-mediated allylation reactions in aqueous media. Both methods gave 3-allyl-3-hydroxycephams in moderate to excellent yields.149... 

Scheme 5.8.18 Tin-mediated allylation with electrochemical recycling...

Scheme 25. Highly f/ireo-sdective tin-mediated allylation of sugars...

A major improvement was realized with the use of indium, a metal with a very low first ionization potential (5.8 eV) which works without ultrasonic radiation even at room temperature [87]. As the zero-valent indium species is regenerated by either zinc, aluminum, or tin, a catalytic amount of indium trichloride together with zinc, aluminum [88], or tin [89] could be utilized in the allylation of carbonyl compounds in aqueous medium. The regeneration of indium after its use in an allylation process could be readily carried out by electrodeposition of the metal on an aluminum cathode [90], Compared with tin-mediated allylation in ethanol-water mixtures, the indium procedure is superior in terms of reactivity and selectivity. Indium-mediated allylation of pentoses and hexoses, which were however facilitated in dilute hydrochloric acid, produced fewer by-products and were more dia-stereoselective. The reactivity and the diastereoselectivity are compatible with a chelation-controlled reaction [84, 91]. Indeed, the methodology was used to prepare 3-deoxy-D-galacto-nonulosonic acid (KDN) [92, 93], N-acetylneuraminic acid [93, 94], and analogs [95],... 

Recently, nanometer tin-mediated allylation of aldehydes or ketones in distilled or tap water gave rise to homoallyl alcohols in high yield without any other assistance such as heat or supersonic or acidic media (Eq. 8.41). Allylation of P-keto aldehydes and functionalized imines by diallyltin dibromide was carried out to generate skipped and conjugated dienes. Aldehydes are allylated with CH2=CHCH2SnBu3 using Sn catalysts in acidic aqueous media. Exclusive aldehyde selectivity was observed for competitive reactions of aldehydes and ketones in the presence of 5 mol% of (CH2=CHCH2)4Sn or SnCU in a mixture of aqueous HCl and THE (Eq. 8.42). ... 

A study on the selectivity of stannylene acetal-mediated alkylation of methyl 4,6-0-benzylidene-a-D-glucopyranoside has concluded that increased bulk of the alkyl groups on tin and a non-polar or no co-solvent increase the proportion of 0-2 mono-ethers formed.The tin-mediated allylation and benzylation of 1,2-0-... 

A full paper has appeared on the tin-mediated allylation and benzylation of 1,2-0-isopropylidene-myo-inositol (see Vol. 27, p. 219, ref. 126 and Vol. 25, p. 215, ref. 108 for preliminary report) which resulted in the preparation of various protected myo-inositol 1,6-bis-and 1,5,6-tris-phosphates. ... 

Unlike the metallic tin-mediated allylation of carbonyl compounds, which requires either acidic medium, aluminum additive, ultrasonic radiation or heating, the metallic zinc-mediated allylation proceeds at room temperature. 

Compared to tin-mediated allylation in ethanol-water mixture, the indium procedure is superior in terms of reactivity and selectivity. Indium-mediated allylation of pentoses and hexoses produced fewer by-products and was more diastereoselective. The reactivity and the lAreo-selectivity, compatible with a chelation-controlled reaction, were even improved when preformed allyl-dichloroindium was allowed to react with ribose in an ethanol-water mixture (Kim et al, 1993). As an application of the indium methodology, a diastereoselective three erythro = 4/1) allylation of /V-acetyl-p-D- mannosamine (Scheme 4.4) with ethyl a-bromomethylacrylate and indiiun in a mixture of ethanol and 0.1 N aqueous hydrochloric add could be achieved, allowing a straightforward synthesis of /V-acetylneuraminic acid, the sialic acid that... 

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