Allyltin compounds addition reactions

Allyltin compounds can be prepared by simple modifications of the usual reaction involving allyl Grignard reagents (139), by the 1,4-addition of trialkyltin hydrides to 1,3-dienes 140,141), or by the reaction of an aldehyde or ketone with the appropriate, tin-carrying, Wittig reagents (142). 

Unsaturated ketones can be readily synthesized by a three-component coupling reaction, comprised of alkyl halides, CO, and allyltin reagents [53]. Because of the slow direct addition of alkyl radicals to allyltin compounds [54], radical carbonylation with allyltin can be conducted at relatively low CO pressures to give good yields of y ,y-unsaturated ketones (Scheme 4-29). 

Allyltin compounds were uniformly shown to be less reactive than the zinc or especially indium analogs. Thus, strongly acidic conditions (HBr, AcOH) were required to perform the heterogeneous reaction using metallic tin, allylic bromides and aldehydes, even if the presence of water accelerated the reaction compared to the reaction in pure diethyl ether. Allylation of ketones required metallic aluminum as an additive [115]. In this way, five- or six-membered rings were prepared through intramolecular reactions (Scheme 24) [116]. 

Driven by the inability to substitute allyltin compounds at the 3-position, Keck examined intermolecular addition reactions of allyl sulfides [50]. He was able to show that 3-methyl- and 3,3-dimethyl-substituted allyl phenyl sulfides 86 and 88 undergo reaction with alkyl halides and alkyl phenyl selenides in the presence of hexabutylditin to form good yields of the allylation products (Scheme 18). These... 

Allyltin compounds behave as excellent unimolecular chain transfer (UMCT) reagents [49] which serve as radical acceptors and sources of tin mediators [50]. Since acyl radicals are nucleophilic radicals, the addition reaction to allyltin, which is regarded as an electron rich alkene, is not a rapid process. Ryu, Sonoda, and coworkers found that unsaturated ketones can be synthesized by a three-component coupling reaction, comprised of alkyl halides, CO, and allyltin reagents [51]. Because of the slow direct addition of alkyl radicals to allyltin compounds [50b], radical car-bonylations with allyltin can be conducted at relatively low CO pressures, and high substrate concentrations (0.1-0.05 M) were used to ensure the chain length. 

The addition of allytributyltin to benzaldehyde has been reported to occur efficiently in the presence of Sc + in deaerated MeCN at room temperature. The 1 1 benzalde-hyde-Sc + complex acts as an actual intermediate in the addition reaction of allyltin compounds to benzaldehyde. ... 

Allyltin chlorides, allylSnIL/T-, are more reactive in carbonyl addition than are the allyltrialkylstannanes, allylSnRj, and for this purpose, the latter can be converted into the former by the Kocheshkov redistribution reaction with BuSnCl3 or S11CI4 the /ra r-stannylation can be carried out with the carbonyl compound in situ in a one-pot process (Equation (97)).270... 

Allyltin difluoroiodide, formed in situ by the oxidative addition of stannous fluoride to allyl iodide, is found to react with carbonyl compounds to give the corresponding homoallylic alcohols in excellent yields under mild reaction conditions (9). 

The effect of added LiC104 was studied with five allyltin derivatives in ether, under standard conditions." The results are given in Table 6.3.4. In pure ether, the yields of the studied compounds after 3 h were less than 5%. The yield for allyldi-n-butyltin chloride was equal to 30%. Illumination for a longer time led to decomposition. The addition of 4 mol dm of LiC104 produced a considerable increase in the yield of the reaction no cycladdition products were detected, and the ratio of the M-ene and H-ene reactions varied from ca. 1 1 for allyltricyclohexyltin to 1 0 for allyltriphenyltin. As observed with the azo enophiles, an increase in the polarity of the medium resulted in an increase in the overall rate of the reaction, and a chemoselectivity favoring the M-ene reaction. 

The radical carbonylation of an alkyl iodide in the presence of Kim s sulfonyl oxime ethers [58, 59, 60] provides a new type of multicomponent coupling reaction where plural radical Cl synthons are consecutively combined [61]. In the transformation, allyltin was used to serve as a trap of benzenesulfonyl radical which converts sulfonyl radical to a tin radical, thus creating a chain. Scheme 14 illustrates such an example, where the product was easily dehydroxylated to give the corresponding tricarbonyl compound on treatment with zinc/AcOH. The radical acylation reaction by Kim s sulfonyl oxime ethers can be conducted under irradiation with the addition of hexamethylditin. This is an alternative path for achieving a similar transformation without the use of photolysis equipment. Scheme 15 illustrates several examples where carbon monoxide and Kim s sulfonyl oxime ethers are successfully combined to create new tandem radical reaction sequences [61],... 

Consideration of the mechanism of the catalytic effect of rare earth ions on addition of organometallics to a, 8-unsaturated compounds has included addition of allyl-tributyltin to benzaldehyde catalysed by Sc. Stereospecificity in the Lewis acid-promoted allylation reaction of 3,3-disubstituted allyltins towards aldehydes has been attributed to an acyclic jyn-synclinal transition state. ... 

It is quite remarkable that in most cases CH-acids are added without either primary transformation into enolate forms or even the addition of a base capable of in situ deprotonation. The reaction with CH-acids without prior deprotonation was described for non-aqueous media for the palladium-catalyzed allylation with allyltin derivatives [69], though the mechanism proposed is quite specific and requires the presence of an organotin compound. By adjusting this mechanism to the reaction in water, the process shown in Scheme 5.5 may be considered. 

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