An optically inactive polyacetylene, poly((4-carboxyphenyl)acetylene) (poly-1), exhibits an induced circular dichroism (ICD) in the UV−visible region upon complexation with chiral amines and amino alcohols in DMSO and in the film, the sign of which reflects the stereochemistry including bulkiness, type (primary, secondary, or tertiary), and absolute configuration of the amines. Therefore, the polyacetylene can be used as a novel probe for determining the chirality of amines. Most primary amines and amino alcohols of the same configuration gave the same sign for the induced Cotton effect; however, secondary and/or tertiary amines used in the present study tended to show Cotton effect signs opposite to those of the primary amines and amino alcohols of the same configuration. The magnitude of the ICD likely increases with an increase in the bulkiness of the chiral amines. The complexation dynamics during the formation of the helical structure of poly-1 with chiral amines were investigated on the basis of the...

Chirality Assignment of Amines and Amino Alcohols Based on Circular Dichroism Induced by Helix Formation of a Stereoregular Poly((4-carboxyphenyl)acetylene) through Acid−Base Complexation

The hetero Diels-Alder reaction is one of the most important methods for the synthesis of heterocycles. In this article an overview is given for the period since 1989 describing the reaction of heterobutadienes such as oxabutadienes, thiabutadienes, azabutadienes, diaazabutadienes, nitroso-alkenes and nitroalkenes as well as of heterodienophiles such as carbonyls, thiocarbonyls, imines, iminium salts, azo- and nitroso compounds. In addition, several other less common hetero Diels-Alder reactions such as cycloadditions of thiaazabutadienes, oxaazabutadienes, dioxabutadienes, dithiabutadienes, oxathiabutadienes, diazaoxabutadienes as well as the use of N-sulfinyl-phosphaalkynes and other dienophiles are mentioned. A main point of discussion is the stereoselectivity of the reactions and the preparation of enantiopure compounds either using dienes and dienophiles carrying a chiral auxiliary or employing chiral Lewis acids. A point stressed is the synthesis of natural products using hetero Diels-Alder reactions leading to carbohydrates, alkaloids, terpenes, antibiotics, mycotoxins, cytochalasans, antitumor agents and several other classes of natural products.

Hetero diels-alder reactions in organic chemistry

Control over the preferred helical sense of a poly(n-hexyl isocyanate) (PHIC) by using a single light-driven molecular motor, covalently attached at the polymer's terminus, has been accomplished in solution via a combination of photochemical and thermal isomerizations. Here, we report that after redesigning the photochromic unit to a chiroptical molecular switch, of which the two states are thermally stable but photochemically bistable, the chiral induction to the polymer's backbone is significantly improved and the handedness of the helical polymer is addressable by irradiation with two different wavelengths of light. Moreover, we show that the chiral information is transmitted, via the macromolecular level of the polyisocyanate, to the supramolecular level of a lyotropic cholesteric liquid crystalline phase consisting of these stiff, rodlike polymers. This allows the magnitude and sign of the supramolecular helical pitch of the liquid crystal film to be fully controlled by light.

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Light-controlled supramolecular helicity of a liquid crystalline phase using a helical polymer functionalized with a single chiroptical molecular switch.

Domino-reactions: The tandem-knoevenagel-hetero-diels-alder reaction and its application in natural product synthesis

This Account describes how stereochemical ideas focused on chirality have been directed widely across polymer science allowing experiments that could not be conducted on small molecules and leading to new insights and new kinds of materials. In one approach, a helical polymer was studied, and it was discovered how the chiral information necessary to choose helical sense is greatly amplified. In another approach, the racemization kinetics of atropisomers were used to characterize the restrictions to motion associated with a polyelectrolyte that forms clusters around hydrophobic groups in water and in an entirely different system, the glassy state formed by polymers.

Chiral studies across the spectrum of polymer science.

L'addition d'une enaminone sur l'(ethyl vinyl) ether fournit un dihydro-3,4 pyranne substitue

Intra- and intermolecular hetero-Diels-Alder reactions. 23. Intermolecular hetero-Diels-Alder reactions of enamino ketones at high pressure. The first significant pressure-induced diastereoselectivity in organic transformations

The Hetero Diels-Alder reaction of the enamino ketones 5a–d and ethyl vinyl ether (2) to give the dihydropyrans 6a–d and 7a–d is studied in dichloromethane and in heptane/isodurene under high pressure up to 7 kbar at temperatures between 0.5 and 130°C. The kinetics is measured by on-line FT-IR spectroscopy. The cycloaddition shows a remarkable pressure-dependent increase of diastereoselectivity in favour of the cis adducts 6a–c with the largest effect found for the reaction of 5a and the smallest for 5c. The pressure-averaged overall activation volumes ΔV≠ in dichloromethane are determined to be between –(23.4± 1.0) and –(24.2±1.0) cm3/mol. The ΔΔV≠ values for the cycloaddition of 5a, 5b, and 5c are –(5.9±0.5), –(3.9±0.1), and –(2.4±0.2) cm3/mol, respectively, and the ΔΔH≠ values are –(8.1±1.7), –(8.7±2.7), and –(10.0±0.9 kJ/mol, respectively. Because of the favourable ΔΔV≠ and ΔΔH≠, the selectivity of the reaction of 5a to give 6a/7a can be increased from 1.67: 1.00 at 90°C and 1 bar to 13.6:1.0 at 0.5°C and 6 kbar. This example shows that a significant and synthetic useful increase of diastereoselectivity in chemical reactions is possible by applying high pressure.

Inter- and Intramolecular Hetero Diels-Alder Reactions, Part XXVI. Diastereoselectivity and Kinetics of Intermolecular Hetero Diels-Alder Reactions under High Pressure. A Significant Pressure-Induced Increase in Stereoselectivity

The hetero Diels-Alder reaction of enamino ketone 1 with the vinyl ethers 7–11 leading to the dihydropyrans 12a–e and 13a–e is studied in dichloromethane under high pressures up to 7 kbar. The kinetics is measured by on-line FT-IR spectroscopy up to 3 kbar. For the first time individual rate coefficients kcis and ktrans have been determined. Pressure-averaged activation volumes, 






, for the overall reaction leading to the formation of the two diastereomers in dichloromethane solution between -(19.1 ± 1.7) and -(25.4 ± 1.6) cm3 mol−1 are measured. The corresponding activation enthalpies, ΔH‡, are between (62.2 ± 1.6) and (76.3 ± 3.6) kJ mol−1. The cycloaddition shows a remarkable increase in diastereoselectivity in favour of the cis adducts 12a–e toward higher pressure. The pressure-averaged differences in activation volume, 






, for the two reaction pathways leading to cis and trans diastereomers are found to be between -(4.5 ± 0.3) and -(6.9 ± 0.7) cm3 mol−1. The corresponding differences in activation enthalpy, δδH≠, are between -(4.7 ± 1.4) and -(9.9 ± 1.6) kJ mol−1. Combination of the overall rate coefficient k = kcis + ktrans for the reaction leading to the two diastereomers with the measured product ratio, ccis/ctrans, which is identified with the ratio of the rate coefficients kcis/ktrans, yields the individual coefficients kcis and ktrans. The rate coefficient kcis is strongly influenced by the steric demand of the substituents on both diene and dienophile whereas ktrans varies to a smaller extent, and the observed changes appear to be mainly due to the electronic properties of the substituents.

Inter‐ and intramolecular hetero diels‐alder reactions, 40. Effect of high pressure on the stereoselectivity of intermolecular hetero diels‐alder reactions

The hetero Diels-Alder reaction of 1 and 2 to the 4-aminodihydropyrans 3 and 4 in CH2Cl2 and isodurene solutions is studied between 45°C and 95°C by direct quantitative infrared spectroscopy under high pressure up to 3 kbar. The activation energies in isodurene and in CH2Cl2 are found to be 65 ± 5 kJ · mol−1, and 58 ± 9 kJ · mol−1, respectively. The activation volumes turn out to be practically identical: −25.1 ± 1.7 cm3 · mol−1 in CH2Cl2 and −25.0 ± 1.8 cm3 · mol−1 in isodurene. The promising aspects of applying high-pressure infrared spectroscopy to the detailed kinetic study of organic reactions are indicated.



Inter- und Intramolekulare hetero-Diels-Alder-Reaktionen, XXII. — Infrarotspektroskopische Untersuchung der hetero-Diels-Alder-Reaktion von Enamicarbaldehyden bei hohem Druck



Die hetero Diels-Alder-Reaktion von 1 and 2 zu den 4-Aminodihydropyranen 3 und 4 wird in CH2Cl2 sowie in Isodurol bei Temperaturen zwischen 45°C und 95°C durch quantitative Infrarotspektroskopie unter hohem Druck (bis 3 kbar) untersucht. Die Aktivierungsenergien werden in Isodurol zu 65 ± 5 kJ · mol−1, und 58 ± 9 kJ · mol−1, bestimmt. Fur die Aktivierungsvolumina ergeben sich die fast gleichen Werte von −25.1 ± 1.7 cm3 · mol−1 in CH2Cl2 and −25.0 ± 1.8 cm3 · mol−1 in Isodurol. Es wird auf die vielversprechenden Anwendungsmoglichkeiten der Hochdruck-Infrarotspektroskopie zum detaillierten Studium der Kinetik organischer Reaktionen hingewiesen.

Inter- and intramolecular hetero diels-alder reactions, XXII. hetero diels-alder reactions of enamine carbaldehydes at high pressure studied by on-line IR detection

Winfried Tost

Papers

Intra- and intermolecular hetero-Diels-Alder reactions. 23. Intermolecular hetero-Diels-Alder reactions of enamino ketones at high pressure. The first significant pressure-induced diastereoselectivity in organic transformations

Inter- and Intramolecular Hetero Diels-Alder Reactions, Part XXVI. Diastereoselectivity and Kinetics of Intermolecular Hetero Diels-Alder Reactions under High Pressure. A Significant Pressure-Induced Increase in Stereoselectivity

Inter‐ and intramolecular hetero diels‐alder reactions, 40. Effect of high pressure on the stereoselectivity of intermolecular hetero diels‐alder reactions

Inter- and intramolecular hetero diels-alder reactions, XXII. hetero diels-alder reactions of enamine carbaldehydes at high pressure studied by on-line IR detection