Allylic Tin Reagents

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. 

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>. 

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. 

Chiral Bronsted acids can also promote the asymmetric addition of allylic tin reagents to carbonyl compounds. Baba and coworkers have found that a stoichiometric amount of (fl)-BINOL (37) acts a chiral promoter for the allylation of unactivated ketones with tetraallyltin and in the presence of MeOH, the corresponding nonracemic tertiary homoallylic alcohols are obtained with up to 60% ee [50]. Later, Woodward et al. improved this process and achieved a catalytic enantioselective allylation of aryl ketones by employing (fl)-monothio-binaphthol 36 as a chiral Bronsted catalyst [49]. For instance, in the presence of 20 mol% of the chiral acid 36 and 40 mol% of H20 in toluene, acetophenone (42) was allylated by a 0.7 0.3 mixture of tetraallyltin (41) and butyltriallylltin (55) to give the (jR)-enriched allylated product 56 almost quantitatively with 89-86% ee (Scheme 8). 

Addition to aldehydes. The allylic tin reagent reacts with aldehydes in the presence of BF, ctherate to give preferentially the. vvn-homoallylic alcohol regardless of the geometry of the double bond (10, 411). When carried out in the absence of a catalyst but under high pressure, the reaction results mainly in the a/it/ -isomer. 

Although hexabutyl ditin is readily separated from even moderately polar allylic stannanes by column chromatography, when the allylic tin reagents are nonpolar, removal is often not possible. Frequently small amounts of distannane impurity can be carried on to the addition reaction without an adverse affect on the yield. As the products of the additions are alcohols, subsequent removal of the distannane poses little problem. 

Figure 3.4 The principle of fluorous solid-phase extraction (FSPE). Allylation of 4-trifluoro-methylbenzaldehyde with a fluorous allyl tin reagent and subsequent work-up of the reaction mixture by FSPE. lb the right of the reaction scheme the F NMR spectra of the reaction mixture before and after FSPE purification are shown (figure modified from Ref. [16], courtesy ofThieme Verlag).

The reaction of nucleophiles with 2-alkyl-2-methoxyoxazolidines offers a general method for asymmetric acylation <91T7925>. The 2-methyl derivative reacts with allyl tin reagents in the presence of BF3 to afford the adducts in good yields. Because of the limited stability of the intermediate oxazolium species, the less reactive ally silane reagents give products in only low yield. 

The boron-containing compounds discussed in the previous sections are typical of Type 1 reagents. Also included in this group are reactions of allyl aluminums and uncatalyzed reactions of allyl tin reagents [8,37]. 

Scheme 5. Preparation of C-allyl glycosides by intermolecular addition to allyl tin reagents...

Nishida, M., Tozawa, T., Yamada, K. and Mukaiyama, T. (1996) Asymmetric allylation of aromatic aldehydes using chiral allylic tin reagents. Chemistry Letters, 25,1125-1126 Yamada, K., Tozawa, K., Nishida, M. and Mukaiyama, T. (1997) Asymmetric allylation of carbonyl compounds with tartrate-modified chiral allylic tin reagents. Bulletin of the Chemical Society of Japan, 70, 2301-2308. 

The vast majority of C-C coupling reactions are catalysed by Pd phosphine complexes. Thus, electrogenerated allyl tin reagents couple with allyl halides307 or imidoyl chlorides,308 vinyl tin alkyls and aryldiazonium... 

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