Silylcuprates synthesis

Scheme 3.7. Diastereoselective formation of /S-silyl ( )- or (Z)-ester enolates by silylcuprate conjugate addition followed by alkylation with aldehydes [49]. Stereoselective synthesis of ( )-and (Z)-allyl silanes [50].

Silylcupration also works with 1-aminoalkynes [70], propargyl sulfides [71], prop-argyl amines [14a, 72] - where it has been exploited in the synthesis of saturated and unsaturated y-silyl-a-amino acids (Scheme 3.17) - and propargyl ethers, where... 

Scheme 3.17. Synthesis of functionalized a-amino acids by silylcupration [72a] or stannylcupration [81c] of chiral propargyl amines (Boc = t-butoxycarbonyl TFA = trifluoroacetic acid).

Scheme 3.29. Silylcuprate substitutions in the synthesis of (+)-carbacyclin analogues (TBDMS = t-butyidimethylsilyl) [107].

Scheme 3.31. Synthesis of p-3ra no alcohols by acylation of silylcuprates (Boc = t-butoxycarbonyl) [114d, llSaj.

Scheme 3.32. Synthesis of silylalanines by means of alkyl halide alkylation of silylcuprates [116a].

Scheme 6.37. Allylic substitution with silylcuprates in the course of a prostaglandin synthesis.

The (diastereoselective) conjugate addition of silylcuprate reagents to a variety of chiral derivatives of a,(3-unsaturated carboxylic acids can be used to prepare optically active p-silyl esters.258 259 Best results are obtained with substrates of type (25). The (related) p-silyl ketones, which also constitute valuable building blocks for (acyclic) stereoselective synthesis, are now accessible in high ee via palladium-catalyzed enantioselective 1,4-disiiylation of a,p-unsaturated ketones (Scheme 76).260... 

Another class of /3-lactone enzyme inhibitors that have attracted attention recently is the ebelactones <20020L2043, 20040BC1051>. These compounds are known to be potent inhibitors of esterases, lipases, and aminopeptidases located on cellular membranes. In recent years, synthetic studies have focused on (-)-ebelactone A 141 as the target compound. A total synthesis was reported by Mandal, with key steps being hydroboration of an alkene, a Suzuki-Miyaura cross-coupling, silylcupration of an acetylene, and iodosilylation <20020L2043>. 

The /3-lactone was formed by the cyclization of a 3-hydroxycarboxylic acid with sulfonyl chloride. An alternative synthesis attempted to control all stereochemical relationships in the molecule using the properties of silyl moieties attached to substrates and reagents <20040BC1051>. Stereoselective reactions of this type included the use of silyl groups in enolate alkylations, hydroboration of allylsilanes, and an anti Se2 reaction of an allenyl silane with an aldehyde and ry -silylcupration of an acetylene. The /3-lactone was again formed by the standard sulfonyl chloride cyclization method. 

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