Chiral 2,2‘-Bipyridine-Type N-Monoxides as Organocatalysts in the Enantioselective Allylation of Aldehydes with Allyltrichlorosilane

Abstract

[reaction: see text] The Sakurai-Hosomi-type allylation of aromatic and heteroaromatic aldehydes can be catalyzed by the new heterobidenate bipyridine monoxide PINDOX with high enantioselectivities. The sterochemical outcome is mainly controlled by the axial chirality in PINDOX, which in turn is determined by the annulated terpene units.

Simple and Fast Synthesis of New Axially Chiral Bipyridine N,N′‐Dioxides for Highly Enantioselective Allylation of Aldehydes

“…Although the enantiodiscriminating properties of both catalysts are comparable with other ones such as those prepared by Kočovský et al [4] (long reaction times and high catalyst loadingd), Hayashi [12] (low ees in the allylation of substrates with electron-withdrawing groups), Andrus [10] (long reaction times), their use has several considerable advantages: i) it is easier to prepare them from a simple starting material (just three steps, no special resolution techniques are required, just simple column chromatography), ii) short reaction times (the reaction is usually finished with 1 h even at À78 8C, iii) low catalyst loads (usually 1 mol%).…”

“…Their popularity stems from the fact that due to the strong donating ability they activate the C À Si bond of halosilanes to such an extent that it reacts with various functional groups. [2] The area of catalytically active N-oxides for the allylation of aldehydes [3] spans from monodentate pyridine N-oxides with additional chelating functional groups such as OMe, [4][5][6][7] nitrogen-containing functionalities, [8][9][10] bipyridine N,N'-dioxides, [11,12] to terpyridine N,N',N''-trioxides. [13] All of these catalysts have pros and cons with respect to substrate specifity, enantioselectivity, catalytic activity, preparation, etc.…”

Allylation of Aldehyde and Imine Substrates with in situ Generated Allylboronates — A Simple Route to Enantioenriched Homoallyl Alcohols.

“…Optical rotation: [α] D 20 = -28.0 (c = 0.67, CHCl 3 ) for 49 % ee; ref. [36] [α] D 20 = -33.2 (CHCl 3 ) for 65 % ee.…”

Hoch effiziente asymmetrische Katalyse durch doppelte Aktivierung von Nucleophil und Elektrophil

“…B. 13 und 14, Kočovský et al verwendeten das 2,2'-Bipyridyl-N-monoxid 15 (R = H, Me) [26] und das Isochinolin-N-Oxid 16 [27] zur Allylierung aromatischer Aldehyde mit Allyltrichlorsilanen. Nach Kočovský et al führen elektronenarme Aldehyde zu hohen und elektronenreiche Aldehyde zu niedrigen ee-Werten bei der Allylierung.…”