Stabilization and activation of dienolates with germanium and tin stereo and regioselective aldol reactions regioselective coupling reactions and regioselective synthesis of amino acid derivatives
Yamamoto, Y.; Hatsuya, S.; Yamada J I.
Journal of Organic Chemistry 55(10): 3118-3128
The reaction of lithium dienolates with tin chlorides BuxSnCl4-x (x = 0, 1, 2, 3) produces the .gamma.-stannylated .alpha.,.beta.-unsaturated esters, whereas in general the same reaction with trimethysilyl chloride gives the O-silylated dienol ethers. Quite interestingly, the reaction of certain lithium dienolates with trimethylgermanium halides produces the .alpha.-trimethylgermylated .beta.-.gamma.-unsaturated esters. Further synthetic applications via the .gamma.-stannyl (Sn-masked dienolates) and .alpha.-germyl (Ge-masked dienolates) derivatives have been studied. Regio- and stereoselective aldol condensations with aldehydes are accomplished with either Lewis acid mediated or tetrabutylammonium fluoride induced reactions of Sn-masked dienolates. Arylation, acylation, and vinylation of dienolates at the .gamma.-position are realized by the palladium-catalyzed reactions of Sn-masked dienolates. The C-C bond formation at the .gamma.-position is achieved by the reactions of Ge-masked dienolates with variety of electrophiles. Either the .alpha.- or .gamma. amino acid derivatives can be prepared with very high regioselectivity by treating diethyl azodicarboxylate with (i) lithium dienolates themselves in certain cases, (ii) Sn-masked dienolates, or (iii) Ge-masked dienolates.