Ketones, reaction with allyltin compounds

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 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 same strategy was applied to radical cabonylation with fluorous allyltin reagents. Propylene-spaced fluorous allyltin reagents 22 were tested as mediators for radical carbonylations the four-components coupling reaction with RX, CO, alkenes and the fluorous allyltin produced the -functionalized i8-aUylated ketones 23 (Scheme 28). Diphasic workup (acetonitrile and FC-72) was successfully carried out to separate the products from the tin compounds. Comparison experiments... 

In attempts to prepare homoallyl alcohol in an environmental friendly process, Andrews and co-workers reported its synthesis using a solvent-free method mediated by tin under ultrasound. Experiments showed that the alcohols were produced in excellent yields with aldehydes but that no products were produced using ketones. However, the existence of toxic allyltin compounds in the final products prevented the method from being applied downstream in fine chemical applications. On the other hand, according to Wang et carbonyl allylation reactions mediated by SnCl2 in aqueous solution without a Lewis acid under ultrasonic irradiation were successfully carried out. 

In Section 12.7.B, the Stille coupling reaction reacted a vinyl tin compound with a vinyl triflate, in the presence of palladium(O). Tetravalent tin complexes add to aldehydes and ketones, in the presence of a Lewis acid. Allyltin complexes are, by far, the most widely used of these compounds.297 a typical example is taken from the work of Keck, in which a chiral aldehyde (455) was treated with allyltributyltin, in the presence of various Lewis acids. S As shown in Table 12.19, a mixture of syn (456) and anti (457) products was obtained. The ratio of 456/457 was dependent on the structure of the R group in 455, the solvent and the Lewis acid.The anti product (457) was obtained by using the tert-butyldimethylsilyloxy derivative (sec. 7.3.A.i) of 455 with 2 equivalents of boron trifluoride in dichloromethane. The syn product is obtained preferentially when the benzyloxy derivative of 455 is used with titanium tetrachloride in dichloromethane.298... 

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