Studies On Asymmetric Hetero-Diels-Alder Reaction Catalyzed By Ramification Of BINOL

Diets-Alder reaction has been one of the cornerstone reactions in organicchemistry for the construction of six-membered rings and the formation ofcarbon-carbon bonds. Asymmetric Hetero-Diets-Alder reaction (HDA) betweenelectron-rich diene with aldehydes can provide a series of dihydropyrans anddihydropyranones which are one of the most important intermediates in thesynthesis of many natural products. Most of researches focused on the HDA reactionbetween Danishefsky diene with aldehydes. To date, there have been some examplesof synthesis of substituted dihydropyrones, while the synthesis of 2,6-disubstituteddihydropyrones has not yet been fully studied.1. A new dimeric BINOL imidazonium has been synthesized.2. We prepared an novel ligand, 3-monosubstituted BINOL [(R)-16] and applied itto the enantioselective reaction.3. In this paper, we described the HDA reaction of aldehydes with diene 26 using 3,3'-substituted BINOL [(R)-15] as chiral ligand. It has been found that the readilyaccessible (R)-15/Ti(Oⁱpr)₄ (1.2:1) complex was a effective catalyst for thisreaction. Aromatic aldehydes afforded the corresponding products in moderateisolated yields (up to 72%) with good enantioselectivities (up to 80% ee).4. Aromatic aldehydes in the presence of TiCl₄/NaOCH₃/(R)-16 (1:4.2:1.2)complex gave the products in higher yields (up to 73%) with betterenantioseletivities (up to 84%).5. The structures of new compound (R)-16 and all HDA reaction products were confirmed by NMR and HRMS.