Catalytic Asymmetric Roskamp Reaction of Silyl Diazoalkane: Synthesis of Enantioenriched α-Silyl Ketone

Abstract

A catalytic enantioselective Roskamp reaction of silyl diazoalkane to synthesize a highly optically active α-silyl ketone from aldehydes is described. In the presence of a chiral oxazaborolidinium ion catalyst, the reaction provides α-chiral silyl ketones with good yields (up to 97%) and high enantioselectivities (up to >99% ee). In addition, a one-pot procedure using an asymmetric Roskamp/reduction strategy gives highly optically active syn-β-hydroxysilane in good yields (up to 94%) with high enantioselectivities (up to 99% ee) and syn stereoselectivities (>20:1).

Diastereoselective Synthesis of 2‐(1,3‐Dioxolanes‐4‐yl)‐4H‐pyran‐4‐ones from 2‐Diazo‐3,5‐dioxo‐6‐ynoates (sulfones) and Aldehydes Based on Tandem Cyclization‐Cycloaddition Strategy

“…For example, oxidation‐cyclization (Scheme a) and tandem cyclization strategies (Scheme b) for the construction of γ‐pyranone core have been disclosed in literatures. The metal‐catalyzed reaction of diazo compound with aldehyde to afford 1,3‐dioxolanes has been investigated; however, poor chemoselectivity or low diastereoselectivity of this reaction was usually observed (Scheme c) …”

Copper-Catalyzed Substitution of α-Triflyloxy Nitriles and Esters with Silicon Nucleophiles under Inversion of the Configuration

“…We have shown here that a range of α-triflyloxy nitriles and esters undergo copper-catalyzed C­(sp 3 )–Si cross-coupling with inversion of the configuration. The resulting enantioenriched α-silylated nitriles had not been accessible before while the present formation of α-silylated esters complements the existing approach by enantioselective carbenoid insertion into Si–H bonds. , …”

Catalytic Asymmetric Darzens‐Type Epoxidation of Diazoesters: Highly Enantioselective Synthesis of Trisubstituted Epoxides

“…The observed stereochemistry for enantioselective formation of trisubstituted α,β‐ Z ‐epoxy ester with COBI catalyst 1 e can be rationalized on the basis of the transition‐state model shown in Figure 2. The coordination mode of the phenyl glyoxal to catalyst 1 e and the enantioselective carbonyl addition of phenyl diazoester are the same as have been observed for the asymmetric Roskamp reaction [12b–e] . In the pre‐transition‐state assembly 4 , shown in Figure 2.…”

“…Recently, our group reported highly enantioselective catalytic tandem reactions of diazo compounds with the chiral oxazaborolidinium ion (COBI) [12, 13] as a Lewis acid catalyst. After forming tetrahedral intermediate through nucleophilic addition of diazo compounds into aldehyde, H‐migration [12a–d] (Roskamp reaction, path a) and C‐migration (path b) [12e] led to the construction of optically active β‐keto ester and the all‐carbon quaternary aldehyde, respectively (Scheme 1 B). However, epoxide products were observed as side products in the case of o ‐fluorobenzaldehyde [12a] .…”