Allyl tributylstannane

In a study of C-allylation of 2-bromo-2-deoxy-pentonolactones using allyl-tributylstannane and a radical initiator, mixtures of C-2-allylated pentono-1,4-lactones were obtained [99]. This may indicate that the selectivity in the reactions discussed above is determined by the cyclopentane ring. 

A variety of allylic tributylstannanes has been synthesized through in situ displacement of allylic mesylates with BusSnLi (Eq. 7) [9]. The method is quite general for primary allylic stannanes. 

A free-radical approach has also been successfully applied to the synthesis of primary allylic tributylstannanes (Eq. 8) [10]. The sequence involves a thermal [3,3] rearrangement of an allylic methyl xanthate then addition of a BusSn radical to the double bond of the derived dithiocarbonate intermediate and subsequent loss of COS in a chain-propagating step. 

Table 40. Additions of a transient oxygenated allylic trichlorostannane derived from a d-benzyloxy allylic tributylstannane.

Later, Marshall extended the scope of the CAB catalyst system to allylic stan-nanes (Scheme 4) [8]. Under the infiuence of a catalytic amount of CAB complex 3 and trifiuoro acetic anhydride, allylic tributylstannane 28 can be added to... 

Guerra, F.M., Mish, M.R., and Carreira, E.M., Versatile, diastereoselective additions of sUyl ketene acetals, allyl tributylstannane, and Me3SiCN to N-acyl pyrazolines asymmetric synthesis of densely functionalized pyrazolidines, Org. Lett. 2 (26), 4265, 2000. 

But before 1980, the foundations for essentially all modern synthetic radical reactions had been laid, sometimes by synthetic organic chemists but more often by physical organic chemists. Kharasch reactions (now often called atom transfer reactions) were known since the 1930s and 1940s, and tributyltin hydride was introduced in the 1960s. In the 1970s, SnAc reactions and redox chain aromatic substitutions (Minisci reactions) were already topical, and allylations with allyl-tributylstannane were first described. In short, there were a number of ways to generate and trap radicals on the one hand, and a number of fundamental transformations of radicals such as addition and cyclization to multiple bonds on the... 

Alkylidene malonate substitute complex (89) undergoes diastereoselective Michael-type additions with a number of nucleophiles including organolithiums, Grignards (5ee Grignard Reagent, allyl tributylstannane, and ketene silyl... 

For transformations based on stannane-mediated radical chain sequences, selenol esters are the precursors of choice owing to their ease of preparation, stabilities, and ability to accomplish Sh2 reactions (see Sect. 3.2.1). However, replacing the selenol esters by thiol esters in these tributyltin hydride- or allyl-tributylstannane-mediated chain reactions would be attractive from a synthetic viewpoint. 

The triple bond of arynes reacts with bis-71-allylpalladium in an amphiphilic fashion (Eq. 16) [14]. The reaction of the aryne precursors 38 with allyl-tributylstannane 3a and allyl chloride 12b in acetonitrile in the presence of 2 equivalents of CsF and 2.5 mol% of Pd2(dba)3 CHCl3-dppf catalyst at 40 °C for 12 h affords the 1,2-diallylbenzenes 39 in good to high yields. The reaction proceeds through the addition of two allyl groups of bis-71-allylpalladium to the benzyne triple bond as shown in 40. 

Stereoselective allylation of secondary radicals is possible when a suitable steric bias is present. For example, the thiocarbonyl compound 41 reacts to give exclusively the exo allylated product 42, in which allyl tributylstannane approaches from the less-hindered convex face of the cyclic radical (4.40). In acyclic substrates high stereoselectivity can be achieved by chelation with a Lewis acid. For example, allylation of the selenide 43 is much more stereoselective in the presence of trimethylaluminium, in which the aluminium alkoxide chelates to the carbonyl group to give the species 44, such that the approach of the allyl stannane is directed to the less hindered face (4.41). 

Related Reagents. Allyl trifluorosilane crotyl trichlorosUane allyl tributylstannane allyl trimethylsilane allylcyclopentadienyl [ 4R,trans)- and (45,rrans)-Q, Q, Q, o -tetraphenyl-l,3-dioxolane -4,5-dimethanolato-0,0 ]titanium fi-allyldiisocaranylborane diisopropyl 2-allyl-l,3,2-dioxaborolane-4,5-dicarboxylate diisopropyl 2-crotyl-l,3,2dioxaborolane-4,5-dicarboxylate fi-allyldi-isopinocampheylborane fi-crotyldiisopinocampheylborane. 

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