Allylstannanes reactions with carbonyl compounds

Epoxides. Allylstannanes react under the influence of Pbl -HMPA with carbonyl compounds such as a,P-epoxy ketones and a-bromoketones give epoxy products. On the other hand, the reaction of l-chloro-3-tributylstannyl-l-propene with aldehydes leads to vinyl-epoxides. 

Allyltrialkoxy- or -tris(dialkylamino)titanium reagents are not capable of chelation-controlled addition reactions with oxy- or amino-substituted carbonyl compounds due to their low Lewis acidity87. To attain chelation control, the application of allylsilanes (Section 1.3.3.3.5.2.2.) and allylstannanes (Section I.3.3.3.6.I.3.2.) in the presence of bidentate Lewis acids like titanium(IV) chloride, tin(lV) chloride or magnesium bromide are the better options. 

The majority of catalytic enantioselective allylation reactions involve the chiral Lewis-acid-catalysed additions of allylsilanes or allylstannanes to carbonyl compounds. Monothiobinaphthol has been used by Woodward et al. as a chiral promoter in the enantioselective catalytic allylation of aryl ketones with impure Sn(allyl)4, prepared from allyl chloride, air-oxidised magnesium and SnCl4. Therefore, the allylation of arylketones in these conditions was achieved very efficiently, since the corresponding allylic alcohols were formed in... 

Stereo specific generation and reactions of allylic alkali and alkaline earth metals have been reviewed121 and solvent-mediated allylation of carbonyl compounds with allylstannanes has been explored.122 Chiral phosphoramides derived from (5 )-proliiie have been used to catalyse asymmetric allylation of aromatic aldehydes by allylic trichlorosilanes.123... 

The Lewis acid-mediated addition of allyl silanes and allyl stannanes to carbonyl compounds has been a topic of interest for many years [103,104]. Stereochemical studies of reactions of allylsilanes and allylstannanes with aldehydes have included FeCl3-mediated intramolecular reactions (Sch. 20) [105],... 

Intramolecular allylation of functionalized allylstannanes is feasible. One application used in the synthesis of natural product is shown in Eq. (108) [282]. The yield is, however, moderate in this example. More examples of titanium-promoted inter- and intramolecular reactions of allylstannanes with carbonyl and related compounds are summarized in Table 10. 

Allylstannanes rapidly undergo the Kocheshkov comproportionation reaction with SnCU, even at -50 °C. The initial product is apparently formed with allylic inversion, but further transmetallation may give other allylic isomers.35 The SnCl3 group which is formed enhances the electrophilic power of the allyl group. This has been exploited in aromatic allylation (equation 9-13),36 and transmetallations of this type provide the basis for some, but not all, of the examples of the catalysis of the allylation of carbonyl compounds by allylstannanes in the presence of Lewis acids37,38 (Section 9.1.3.4). 

The Keck reaction is the allylation of a carbonyl compound performed with an allylstannane and mediated by a Lewis acid. The reaction product is a homoallylic alcohol. 

Carbonyl Allylation and Propargylation. Boron complex (8), derived from the bis(tosylamide) compound (3), transmeta-lates allylstannanes to form allylboranes (eq 12). The allylboranes can be combined without isolation with aldehydes at —78°C to afford homoallylic alcohols with high enantioselectivity (eq 13). On the basis of a single reported example, reagent control might be expected to overcome substrate control in additions to aldehydes containing an adjacent asymmetric center. The sulfonamide can be recovered by precipitation with diethyl ether during aqueous workup. Ease of preparation and recovery of the chiral controller makes this method one of the more useful available for allylation reactions. 

Instead of using a stoichiometric amount of indium, the allylation of aldehydes and ketones can be carried out by using catalytic amounts of indium(III) chloride in combination with aluminum or zinc metals in a THF/water (5 2) mixture at room temperature. The reaction is much slower relative to the same reaction mediated by a stoichiometric amount of indium. When the reaction was carried out in anhydrous THE, the yield dropped considerably, while side reactions (such as reducing to alcohol) increased. The combinations of Al/InCh or Zn/InCh gave comparable results. The indium-mediated allylation carried out with allylstannanes in combination with indium chloride in aqueous medium was reported by Marshall and Hinkle. Allyl indium was proposed as the reaction intermediate. Various allylic compounds undergo palladium-catalyzed allylation of carbonyls via the transmetala-tion of r -allylpalladium(II) intermediates with indium in the presence of indium trichloride in aqueous media. °... 

---