New Pathway to C₂‐Symmetric Atropoisomeric Bipyridine N,N′‐Dioxides and Solvent Effect in Enantioselective Allylation of Aldehydes

Abstract

The [2 + 2 + 2] cyclotrimerization of 1,7,9,15-hexadecatetrayne with nitriles catalyzed by dicarbonylcyclopentadienylcobalt(I) opened a new pathway for the synthesis of C 2 -symmetrical bis(tetrahydroisoquinolines) that were used as starting material for the preparation of axially chiral bipyridine N,N'-dioxides. The N,N'-dioxides (1 mol%) were found to be highly catalytically active and enantioselective (up to 83% ee) for the asymmetric allylation of aldehydes with allyl(trichloro)silane in various solvents. In addition, a dramatic solvent effect was observed where the use of different solvents induced opposite chiralities of the product with the same enantiomer of the catalyst, e.g., 65% ee (S) in acetonitrile (MeCN) vs. 82% ee (R) in chlorobenzene.

Helicity Induction and Its Static Memory of Poly(biphenylylacetylene)s Bearing Pyridine N‐Oxide Groups and Their Use as Asymmetric Organocatalysts

“…The reason for this inversion of the enantioselectivity of hm (R)5 -poly-2b depending on the substrates (3a and 3c) (entries 6 and 8 in Table 1) is not clear at present, but may be due to the electron-withdrawing nitro-substituent of 3c. A similar inversion of the enantioselectivity depending on the substrates was reported by Kotora et al 65 The fact that hm (S)5 -poly-2b with an opposite-handed helicity memory produced the product with the opposite configuration (8% ee (S-rich)) while maintaining its catalytic activity (entry 9) demonstrated that optically active helical polymers bearing achiral, but catalytically active residues as the pendants whose optical activities are solely derived from their static helicity memory indeed work as asymmetric catalysts, leading to the development of switchable asymmetric catalysts.…”

Heteroaromatic N-Oxides in Asymmetric Catalysis: A Review

“…Researches mainly concentrate on symmetrically or unsymmetrically substituted chiral bis(tetrahydroisoquinoline) N,N'-dioxides ( Figure 7), which with their structure resemble compound 8. In 2008 Kotora et al synthesized symmetrically substituted by (R)-tetrahydrofuran-2-yl dioxides 32 (see Figure 7), which were tested in the allylation of aromatic [50] as well as aliphatic aldehydes [30]. Catalysts synthesis was based on cyclotrimerization of tetrayne with (R)-tetrahydrofuran-2-carbonitrile, followed by oxidation of received bipyridines by m-CPBA.…”

Enantioselective Allylation of Aldehydes Catalyzed by Diastereoisomeric Bis(tetrahydroisoquinoline) N,N′‐Dioxides

“…Gratifyingly, the presence of substituents in the α-position (chloro and methyl groups) to the carbonyl group in 4f and 4g led to products 5f and 5g with high enantioselectivity (96 % ee; Table 3, Entries 6 and 7), which was higher than those obtained previously. [26] The allylation of aliphatic α,βunsaturated aldehydes 4h and 4i bearing a methyl group at the α-position led to products 5h and 5i with ee values of 70 and 80 % ee, respectively.…”

“…[23] Recently, this laboratory developed a procedure for the synthesis of various axially chiral N,NЈ-dioxides with the bipyridine scaffold based on CpCo(CO) 2 -catalyzed [2+2+2]-cyclotrimerization of alkynes (diynes) with nitriles under microwave irradiation. These included axially chiral pyridyl(tetrahydroisoquinoline)s, [22] isoquinolyl(tetrahydrosioquinoline)s, [25] symmetrically 3,3Ј-substituted bis(tetrahydroisoquinolyl)s, [26] and unsymmetrically 3,3Ј-substituted bis(tetrahydroisoquinolyl)s. [27,28] Unsymmetrically 3,3Ј-substituted bis(tetrahydroisoquinolyl)s, in particular, were proven to catalyze the highly enantioselective allylation of aromatic and α,β-unsaturated aldehydes with ee values reaching up to 99 %.…”

“…[29] These observations and results thus provided the necessary background to understand the high level of asymmetric induction observed for allylations carried out in THF. [27a,28] Taking into account the easy and fast preparation of (R,R ax ,R)-and (R,S ax ,R)-bis-1,1Ј-[5,6,7,8-tetrahydro-3-(tetrahydrofuran-2-yl)isoquinoline] N,NЈ-dioxides (1; [26] Figure 1) and the above-mentioned solvent effects, we decided to screen the enantioselective allylation of aromatic aldehydes in detail and also to check its scope in the case of α,β-unsaturated benzaldehydes.…”