Intramolecular rearrangement with ring contraction of 1,4-dihydroxy-3-bromo-2,2,6,6-tetramethylpiperidine

SummaryThe thermo-oxidative decomposition of lovage (Levisticum officinale) and davana (Artemisia pallens) essential oils has been studied by pyrolysis-gas chromatography/mass spectrometry in 9% oxygen and 91% nitrogen atmosphere at 300 °C to simulate low-temperature tobacco heating conditions. Both lovage and davana oils contain numerous chemical substances; the main components of both oils are various oxygen-containing compounds. Isobenzofuranones are the most important constituents of lovage oil, and their relative intensity changed significantly during oxidative pyrolysis. (Z)-ligustilide underwent two kinds of decomposition reactions: an aromatization reaction resulting in the formation of butylidenephthalide and the scission of the lactone ring with the elimination of carbon dioxide or carbon monoxide. Davanone is the main component of davana oil, which did not decompose considerably during low-temperature oxidative pyrolysis. However, the relative yield of the second most intensive component, bicyclogermacrene, reduced markedly due to bond rearrangement reactions. Davana ether underwent oxidation reactions leading to the formation of various furanic compounds. The changes in the composition of both essential oils could be interpreted in terms of bond splitting, intramolecular rearrangement mechanisms and oxidation reactions of several constituents during low-temperature oxidative pyrolysis. The applied thermo-oxidative method was found to be suitable to study the stability of the essential oils and monitor the decomposition products under simulated tobacco heating conditions. In spite of the complicated composition of the essential oils, no evidence for interaction between the oil components was found. [Beitr. Tabakforsch. Int. 29 (2020) 27–43]

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ChemInform Abstract: LIGHT-INDUCED REACTION OF BORACYCLANES WITH BROMINE IN THE PRESENCE OF WATER, RING CONTRACTION OF BORACYCLANES TO PRODUCE CARBOCYCLIC STRUCTURES

Chemischer Informationsdienst ◽

10.1002/chin.197405235 ◽

1974 ◽

Vol 5 (5) ◽

pp. no-no

Author(s):

Y. YAMAMOTO ◽

H. C. BROWN

Keyword(s):

Ring Contraction ◽

Water Ring ◽

Induced Reaction

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The Influence of Anomeric Configuration and Aglycone Structure on the Outcome of Acid‐Promoted Ring Contraction in 2,3‐Di‐ O ‐Silylated S‐Galactopyranosides

ChemistrySelect ◽

10.1002/slct.202101441 ◽

2021 ◽

Vol 6 (24) ◽

pp. 6223-6229

Author(s):

Polina I. Abronina ◽

Alexander I. Zinin ◽

Nelly N. Malysheva ◽

Maxim Y. Karpenko ◽

Natalya G. Kolotyrkina ◽

...

Keyword(s):

Ring Contraction ◽

Anomeric Configuration

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ChemInform Abstract: STEREOCHEMICAL NONRIGIDITY IN SOLID ZIRCONIUM AND HAFNIUM TETRAKISTETRAHYDROBORATES. EVIDENCE FOR TWO DYNAMIC INTRAMOLECULAR REARRANGEMENT PROCESSES IN COVALENT TRIDENTATE TETRAHYDROBORATES

Chemischer Informationsdienst ◽

10.1002/chin.197808001 ◽

1978 ◽

Vol 9 (8) ◽

Author(s):

I.-S. CHUANG ◽

T. J. MARKS ◽

W. J. KENNELLY ◽

J. R. KOLB

Keyword(s):

Intramolecular Rearrangement ◽

Stereochemical Nonrigidity ◽

Rearrangement Processes

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N-Chlorinative Ring Contraction of 1,4-Dimethoxyphthalazines via a Bicyclization/Ring-Opening Mechanism

Synthesis ◽

10.1055/s-0040-1706639 ◽

2020 ◽

Author(s):

Jeong Kyun Im ◽

Ilju Jeong ◽

Jun-Ho Choi ◽

Won-jin Chung ◽

ByeongDo Yang ◽

...

Keyword(s):

Ring Opening ◽

Reaction Conditions ◽

Ring Contraction ◽

Silyl Group ◽

Favorskii Rearrangement ◽

Mechanistic Analysis ◽

Group A ◽

Overall Efficiency ◽

Trichloroisocyanuric Acid

AbstractAn unprecedented N-chlorinative ring contraction of 1,2-diazines was discovered and investigated with an electrophilic chlorinating reagent, trichloroisocyanuric acid (TCICA). Through optimization and mechanistic analysis, the assisting role of n-Bu4NCl as an exogenous nucleophile was identified, and the optimized reaction conditions were applied to a range of 1,4-dimethoxyphthalazine derivatives. Also, an improvement of overall efficiency was demonstrated by the use of a labile O-silyl group. A bicyclization/ring-opening mechanism, inspired by the Favorskii rearrangement, was proposed and supported by the DFT calculations. Furthermore, the efforts on scope expansion as well as the evaluation of other electrophilic promoters revealed that the newly developed ring contraction reactivity is a unique characteristic of 1,4-dimethoxyphthalazine scaffold and TCICA.

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