Phosphine Oxide-Catalyzed Enantioselective Intramolecular Aldol Reaction via Regioselective Enolization of Unsymmetrical Diketones with Tetrachlorosilane

Abstract

The phosphine oxide-catalyzed asymmetric intramolecular aldol reactions of diketones were investigated. The combination of tetrachlorosilane and a chiral phosphine oxide catalyst promoted the acetyl-selective enolization of diketones, and the subsequent intramolecular aldol reaction occurred in an enantioselective manner. The introduction of two trimethylsilyl groups at the 4- and 4'-positions in BINAP dioxide catalyst improved the enantioselectivity. This reaction provides an effective synthetic method to access β-tertiary-hydroxy cyclohexanones in high yields and with high enantioselectivity.

Hydrogenation/Hydrolytic Ring Opening of 5-HMF by Cp*-Iridium(III) Half-Sandwich Complexes for Bioketones Synthesis

“…23−27 Diketone derivatives have been used to prepare valuable chemicals, such as alcohols, amines, cycloketones, pyrrolidine, and so forth. 28,29 Very recently, the direct conversion of 5-HMF 30,31 and its derivatives to produce biodiketone derivatives 1-hydroxyhexane-2,5-dione (HHD) by hydrogenation/hydrolytic ring opening reaction was reported on the basis of a Pd/C heterogeneous catalyst system with CO 2 /H 2 O as the acid for the ring opening of furan, resulted in 77% yield HHD from 5-HMF. 32 Ohyama et al reported supported Au nanoparticles, another heterogeneous catalyst, that converted 5-HMF to HHD (60% yield) with the aid of H 3 PO 4 .…”

TetraPh-Tol-BITIOPO: a new atropisomeric 3,3′-bithiophene based phosphine oxide as an organocatalyst in Lewis base-catalyzed Lewis acid mediated reactions

“…Finally, the direct double aldol reaction between acetophenone (11) and benzaldehyde mediated by the presence of SiCl 4 was also explored. Double aldol product was isolated as diacetate form in good yield and 86:14 ratio between the chiral isomer 12-chiro and the achiral 12-meso stereoisomers, with 60% ee for the chiral one (it must be noted that 12-meso is an achiral molecule that may exist in two diastereoisomers, however in this case only one form was observed by 1 H-NMR.…”

Phosphine Oxide-Catalyzed Asymmetric Aldol Reactions and Double Aldol Reactions

“…The hypervalent silicon complex also efficaciously mediated the intramolecular aldol reaction of 2,6-diketones to give β-hydroxycyclohexanones in high yield and with high enantioselectivity. 57)…”