Phosphahelicenes in Asymmetric Organocatalysis: [3+2] Cyclizations of γ‐Substituted Allenes and Electron‐Poor Olefins

Abstract

The first use of phosphahelicene in enantioselective organocatalysis is reported. New chiral phosphahelicenes have been prepared and enable highly enantioselective [3+ +2] cyclization reactions between arylidene-or alkylidenemalononitriles and g-substituted allenoates or cyanoallenes.T hese reactions affordc yclopentene derivatives in both high yields and diastereoselectivities,w ith enantiomeric excesses of up to 97 %.

Helicene Radicals: Molecules Bearing a Combination of Helical Chirality and Unpaired Electron Spin

“…[31] The enantiomers of 14 were separated by HPLC owing to the enough racemization barrier (exp. 112.8 kJ/mol) irrespective of the [4]helicene motifs. The cyclic voltammetry measurement of 14 indicated two oxidation processes separated by a relatively large gap.…”

“…Triarylamines are important electron donors that have been extensively utilized in fundamental chemistry and technology of organic electronic devices. [27] S. Menichetti et al prepared thia-bridged triarylamine [4]helicenes 12 [28] that are also regarded as phenothiazine dimers wherein a phenyl ring and a nitrogen atom are shared (Figure 2, Table 2). Phenothiazine derivatives have also been often applied as electron donors in photo-redox systems and organic electronic devices.…”

“…Phenalenyl that is a planar neutral π-radical with delocalized electronic spin over its hydrocarbon framework has been utilized to construct a lot of functional open-shell molecules (Figure 3, Table 3). [35] Based on diazaphenalenyl scaffold, T. Takui and Y. Morita et al prepared a [4]heterohelicene 16 as a neutral radical, [36] which was the first example of an isolated air-stable helicene radical, irrespective of the absence of its crystallographic analysis and magnetic susceptibility measurement. 492, 565, 593, 668, 778, 1017, 1304, 1604 [40] [a] λ max values in parentheses are estimated from the absorption spectra by the authors of this review.…”

“…B. W. Laursen and co-workers also employed similar diaza unit to synthesize a [4]heterohelicene neutral radical 17, wherein the two nitrogen atoms were alkylated (Figure 3, Table 3). [37] The neutral radical of 17 was formed by in-situ electrochemical reduction of the cationic precursor, but not isolated due to its less stability.…”

“…Chiral helicene compounds that have helical π-conjugated frameworks comprised of ortho-fused aromatic rings have been intensively investigated for several decades [1] owing to their attractive properties and high potentials for a variety of applications such as chiroptical responses, [2] molecular recognition, [3] asymmetric catalysis, [4] etc. As for chiroptical properties, extended π-conjugation of helicenes affords very large optical rotation (OR) values, strong electronic circular dichroism (ECD) spectra [5] and meaningful circularly polarized luminescence (CPL).…”