Expeditious Synthesis of Benzopyrans via Lewis Acid-Catalyzed C−H Functionalization: Remarkable Enhancement of Reactivity by an <i>Ortho</i> Substituent
An expeditious construction of a benzopyran skeleton via Lewis acid-catalyzed C−H functionalization was achieved. In this process, a [1,5] hydride shift and 6-endo cyclization successively occurred to give benzopyrans. The presence of substituents ortho to the alkoxygroup significantly enhanced the reactivity, affording the desired compounds in excellent chemical yields with short reaction times.
Chiral Zirconium Catalysts Using Multidentate BINOL Derivatives for Catalytic Enantioselective Mannich-Type Reactions; Ligand Optimization and Approaches to Elucidation of the Catalyst Structure
Catalytic enantioselective Mannich-type reactions of silicon enolates with aldimines were investigated using chiral zirconium catalysts prepared from Zr(O(t)Bu)(4), N-methylimidazole, and newly designed multidentate BINOL derivatives. These new multidentate BINOL ligands were designed on the basis of an assumed transition state structure of a chiral zirconium catalyst derived from two molecules of
useful for syntheses of catechol derivatives, it is hampered by many competing reactions and has not been developed as a useful methodology. Here, we succeeded in settling this problem by a first systematic thorough investigation, establishing the 1,2-rearrangement as a cascade reaction with a retro Diels-Alder reaction from o-quinol dimers. This is a useful strategy for syntheses of substituted catechols