Chemistry of carbanions. XXIII. Use of metal complexes to control the aldol condensation

Syntheses and Antimicrobial Activity of Tetrasubstituted Tetrahydrofuran Lignan Stereoisomers

“…The silica gel used was Wakogel C-300 (Wako, 200-300 mesh). (12). To an ice-cooled solution of 11 (17.3 g, 0.042 mol) and 2,6-lutidine (8.43 ml, 0.072 mol) in CH 2 Cl 2 (200 ml) was added TIPSOTf (14.4 ml, 0.054 mol).…”

“…Selective deprotection of the secondary hydroxy group under acidic conditions, followed by OsO 4 oxidation, NaIO 4 oxidation, and pyridinium chlorochromate oxidation gave lactone 21. After aldol condensation using lithium diisopropylamide, the hydroxy group of the resulting aldol mixture (erythro=threo ¼ 1=4; coupling constant of the new benzylic proton: erythro, J ¼ 4:4 Hz; threo, J ¼ 7:2 Hz) 12) was protected as a triethylsily ether, giving pure threo product 22. LiBH 4 reduction followed by tert-butyldiphenylsilyl protection of the primary hydroxy group gave benzyl alcohol 23.…”

“…The aldol condensation of this lactone 29 with piperonal, using potassium bis(trimethylsilyl)amide, gave the corresponding aldol product as a 5/1 mixture of erythro and threo (coupling constant of the new benzylic proton: erythro, J ¼ 2:9 Hz; threo, J ¼ 6: 8 Hz). 12) The LiBH 4 reduction of the aldol mixture, followed by protection of the resulting primary hydroxy group as a tert-butyldiphenylsilyl ether gave separable benzyl alcohol derivatives 1S-30 and 1R-31. The partially separated major erythro aldol product could be converted to 1S-30.…”

The relative configuration of 8-[(2,2-dimethyl-3-oxocyclohexyl)hydroxymethyl]-1-methylbicyclo[4.2.0]octan-7-one, C18H28O3

“…non-hydrogen atoms Young, 1981;House, Crumrine, Teranishi & Olmstead, 1973). The rationale for doing this is that the aldol itself should exist in solution as a six-membered ring in which the hydroxyl hydrogen atom hydrogen bonds to the ketone.…”

Acetate-Promoted Aldol-Type Reaction: Scope and Reactivity of Acetates and Aldehydes

“…1a To overcome such limit, several indirect methods such as employing silyl enol ether, 22 2-formylketone, 23 enamine, 24 lithiated imine, 25 and lithiated enamine, 26 have been designed, but sometimes long reaction sequence and expensive reagents are the bottle-necks for the general use.…”