Allylation aldehydes with allylstannane catalyzed

Scheme 13.9 Allylation of aldehydes with allylstannane catalyzed by Yb(OTf)3.

The chiral titanium complex BINOL-T1CI2 also catalyzes the asymmetric carbonyl addition reaction of allylic silanes and stannanes. Thus the addition reaction of glyoxylate with (E)-2-butenylsilane and -stannane proceeds smoothly to give the syn product in high enantiomeric excess (eq 12). The syn product thus obtained can be readily converted to the lactone portion of verrucaline A. The reaction of aliphatic and aromatic aldehydes with allylstannane is also catalyzed by BINOL-TiC to give... 

Addition to C=0. Hydrates of a-ketoaldehydes react selectively at the aldehyde group with allylsilanes under the influence of YbfOTfjj at room temperature. The allylation of aldehydes with allylstannanes is accelerated by benzoic acid." Another method for the synthesis of homoallylic alcohols is by the ene reaction, thus y,6-unsaturated a-hydroxy esters are obtained from glyoxylic esters at room temperature in a catalyzed process. ... 

A chiral phosphine-silver(I) complex generated from BINAP and AgOTf-catalyzed asymmetric allylation of aldehydes with allylstannanes, resulting in high enantioselectivity. With 2-butenylstannane, the anti adduct was obtained preferentially irrespective of the double-bond geometry of the stannane (Scheme 12.28) [76]. 

Asymmetric allylation of aldehydes with allyhc agents catalyzed by Lewis acid is a practical method for synthesizing optically active hranoallylic alcohols [10]. The chloro complex 1 serves as an efficient catalyst for asymmetric allylation of aldehydes with allylstannane [8, 9, 11]. In the presence of 5 mol% of the benzyl-phebox-Rh complex 1-Bn, the coupling reaction of benzaldehyde with allyltributyl-stannane in CH2CI2 at room temperature proceeded smoothly to provide the corresponding homo-aUyl alcohol 7a in 88% yield with 61% ee (Scheme 2). When methaUylstannane was subjected to the reactiOTi, enantioselectivity of the allylated product 8 significantly increased to be over 90% ee. 

Bis-pi-allyl Pd and Pt complexes have been found to catalyze the addition of allyl tributyltin to aldehydes [26]. These catalysts are formed in situ from Pd- and PtCl2-phosphine complexes and the allylstannanes (Fig. 7, step 1). The allylation step is depicted as a metallocene reaction of the aldehyde and an his-allylmetal complex (Fig. 7, step 3). The catalyst is regenerated by attack of the allylic stannane on the alcoholate-palladium complex formed in step 3. Representative additions of allyl and methallyl tributyltin to aldehydes with the pi-allyl platinum catalyst are summarized in Table 14. 

Mechanistic studies of the allylic transfer have been performed, and synthetic application of allylstannanes in organic synthesis has been inveshgated. B(C6F5)3 has been shown to catalyze discriminative allylahon of aldehydes with an ortho donor substituent in preference to the para isomer, and the role of B(C6F5)3 has... 

Allylstannanes with another stannyl group proved of great utility for further C-C bond formation [28]. Consecutive allylation of a non-racemic epoxy-aldehyde with the allylic bis-stannane followed by palladium-catalyzed coupling of the resulting ethenyltin with vinyl iodide was exploited in a total synthesis of (-i-)-amphidinohde K (Scheme 12.9) [29]. 

Scheme 10.4 Allylation of a,p-unsaturated W-acylpyrroles and aldehydes with allylboronic esters and allylstannanes catalyzed by an NHCP palladium allyl complex.

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. °... 

Use of di-M-butylstannyl dichloride along with an acyl or silyl halide leads to addition of allylstannanes to the aldehydes.106 Reaction is also promoted by butylstannyl trichloride.107 Both SnCl4 and SnCl2 also catalyze this kind of addition. Reactions of tetraallyl-stannane with aldehydes catalyzed by SnCl4 also appear to involve a halostannane intermediate. It can be demonstrated by NMR that there is a rapid redistribution of the allyl group.108... 

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