Dilithium catecholate

A similar reducing system is created by combining dilithium catecholate and trichlorosilane at —78° in tetrahydrofuran. It is speculated that the relatively unstable pentacoordinate bis(l,2-benzenediolato)hydridosilicate (61) is formed in situ and that it is this species that can reduce aldehydes and ketones, but not esters, to alcohols when they are added to the reaction mixture at 0° (Eq. 168).93 In a like manner, the dilithium salt of 2,2/-dihydroxybiphenyl, which forms a pentacoordinate intermediate that is stable enough to react at room temperature, can also be used to promote the reduction reaction. The alkoxides of aliphatic diols... 

Stereoselective reaction with aldehydes. Both (E)- and (Z)-l react with aldehydes to give syn-adducts as the major products (12,146). In an effort to improve the diastereoselectivity, (E)- and (Z)-l have been converted into pentacoordinated allylsilicates (2) by reaction with dilithium catecholate. Reaction of an aryl aldehyde with both (E)- and (Z)-2 shows essentially complete diastereoselectivity. 

Evidence for a closed transition-state model was gathered on the basis of the diastereoselectivity in reactions of pentacoordinate allylic silicates. Bis(l,2-benzenediolato)allylsilicates la and lb, which can be prepared via the reactions of E- and Z-crotyltrichlorosilanes with dilithium catecholate, react with aromatic aldehydes to give the corresponding homoallylic alcohols 2 in high yields3 (Scheme 3.2a). Unlike allyltrimethylsilane,4 the allylation reactions of... 

Sakurai pioneered the field of nucleophilic activation of reagents 21.5 by employing stoichiometric amounts of CsF or dilithium catecholates for highly diastereoselective allylation of aldehydes with allyltrihalosilanes 21.5. Later, it was demonstrated that the common dipolar aprotic solvents possessing a strongly Lewis basic ojg gen promote the allylation reaction. Thus, Kobayashi revealed that DMF can act both as a solvent and a Lewis-base activator. Denmark further established that, in contrast to DMF that was required in large excess to promote the allylation of aldehydes, HMPA can be used in substoichiometric quantities. 

Treatment of 2 with the disodium salt of catechol afforded one of the first structurally characterised examples of a diborane(4) compound with a bridging diolate, namely 1,2-B2(NMe2)2(cat) (6). In contrast, the reaction between 2 and the dilithium salt of thiocatechol afforded the 1,1-isomer, l,l-B2(NMe2)2(thiocat) (7) as the major product... 

H2O, stable for a few days at -S ". This reagent is prepared by the reaction of SF4 and the dilithium salt of catechol. 

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