Hydroalumination chemoselectivity

This chapter has been organized into three sections. The first section deals with transition metal-catalyzed hydroboration in organic synthesis and this is divided into three subsections - mechanism, chemoselectivity, and stereoselectivity. The second section deals with the application of transition metal-catalyzed hydroalumination reactions in organic synthesis, and this is also divided into three subsections - mechanism, chemoselectivity, and stereoselectivity. The third section examines the application of both hydroborations and hydroaluminations in total synthesis. 

Hydrido(trialkylsilyl)silyllithiums, preparation, 3, 424 Hydroacylations, olefins, 10, 142 Hydroalkoxylations and etherification, 10, 672 in etherification, 10, 683 Hydroaluminations for C-E bond formation characteristics, 10, 857 chemoselectivity, 10, 859 mechanism, 10, 858 overview, 10, 839-870 stereoselectivity, 10, 861 total synthesis applications, 10, 865 characteristics, 3, 275 process and examples, 9, 268 via Ti(IV) complexes, 4, 658 Hydroaminations actinide-catalyzed, 4, 237 in aminations... 

The availability of the Schwartz s reagent Cp2Zr(H)Cl (see Schwartz s Reagent) and its versatile behavior explain its extensive use in orgaiuc chemistry. The scope of hydrozirconation (see Hydrozirconation) with respect to both substrate structure and chemoselectivity lies somewhere between those of hydroboration (see Hydroboration) and hydroalumination. 

Finally, the high locoselectivity or chemoselectivity of hydroalumination toward substrates having both C==C and C C bonds is exemplified by the reaction of diisobutylaluminum hydride with 1-octen-7-yne (7). The only organoaluminum product detected (8) was that of a regioselective syn stereospecific addition to the bond (equation 3). 

Other than transition metals, organoboron compounds also catalyzed hydroalumination (Scheme 6.140). Regio- and chemoselectivity was extremely good [180]. 

Hydroalumination Reactions. DIBAL reacts with alkynes and alkenes to give hydroalumination products. Syn additions are usually observed however, under appropriate conditions, equilibration to give a net anti addition is possible. If the substrate has both an alkene and an alkyne group, then chemoselectivity for the alkyne is observed (eq 26). ... 

Despite the low intrinsic reactivity of alkylboranes, Pd-catalyzed all lation with alkylboron compounds holds considerable promise as a unique and chemoselective alkylation method. It is unique in part because hydioboration of alkenes is by far the most general and dependable method for stoichiometrically converting alkenes into organometals and in part because alkylboron compounds thus generated can satisfactorily participate in Pd-catalyzed alkylation under basic conditions. In this connection, it should be noted that the current scopes of hydroalumination and hydiozirconation of alkenes are much more limited than... 

Cp2ZrH(Cl) = ([Zr]-H) reacts with unsaturated C—C bonds to give isolable addition products (in opposition to boranes and alanes, organo-Zr are rather stable in dry air) that can be hydrolyzed with diluted acidic solutions. The scope of hydrozirconation with respect to chemoselectivity and substrate structure lies between those of hydroalumination and hydroboration. The facile isomerization of secondary alkylzirconium derivatives into primary alkyl derivatives occurs very readily (even below room temperature, note the difference with A1 and B ). 

---