Alkoxy groups cyanide exchange

Scheme 1 shows the desired Heck reaction of alkoxy-DSB 1 with 2. The formation of 3 is accompanied by two destructive pathways the reductive debromination of 1 to 4 as a side reaction and the protodesilylation to 5 as a subsequent reaction. Particularly the latter limits the reaction conditions in terms of time and temperature. The phosphine is a decisive factor in this system consisting of three reactions a fine-tuning of the reaction conditions is possible via electronic and steric effects of the substituents in the phosphine electron-rich trialkylphosphines 6 and 7 strongly favor the reduction. Fast coupling reactions were observed with tris-o-tolylphosphine 8, the chelating diphosphine dppe 9 being even more efficient in terms of turnover, yield, and suppression of side reactions. Compared with Heck reactions of polycyclic or electron-deficient arenes with 2 [21, 22], the yield of 3 is only moderate. The reactivity of bromo-distyrylbenzenes 1 and 12 -14 in the coupling reaction is controlled by the substituents on the opposite side of the n-system (Fig. 1, Table 2) a compensation for the electron-donating alkoxy groups by a cyanide (13) or exchange of donors with electronically neutral alkyl side chains strongly improves the yields.

The exchange of alkoxy groups for the cyanide function can also be achieved in acetals (cyclic types like dioxolanes and 1,3-dioxane derivatives included), 5A -acetals and ortho esters with the combination of TMS-CN/Lewis acids, or under neutral conditions with transition metal salts as catalysts (Scheme 16). Furanose derivatives may be treated with TMS-CN in a similar way. ... 

Orthocarbonates and their analogs do exchange just one alkoxy group with TMS-CN/SnCU (Scheme 17). In earlier pt rs even the direct reaction with HCN and ZnCb at room temperature was reported to give (after several days or even some weeks) high yields. Treatment with acetyl cyanide (Scheme 17) represents another possibility for transforming orthoesters into bisalkoxynitriles. ... 

An elegant procedure for generating ct-cyano ethers from acyclic or cyclic acetals and ketals is their reaction with r-alkyl isocyanides in the presence of an equimolar amount of TiCU (Scheme 18). 72 7]je exchange of alkoxy groups against cyanide functions proved to be very important for the preparation of cyanoquinones. ... 

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