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Dehydration Reaction of β-Oxo Oximes: Synthesis of Isoxazoles and Pyrazolin-5-ones

Author: FuXiaoLan
Tutor: DongDeWen
School: Northeast Normal University
Course: Organic Chemistry
Keywords: Oximes Appel Agents P-toluenesulfonyl Chloride Isoxazoles Pyrazolone
CLC: O621.25
Type: Master's thesis
Year: 2011
Downloads: 78
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Abstract


Oximes chemistry, which derived from 1864, was of importance to organicchemistry during the past 100 years. Primarily, oximes are prepared by simplecondensation of the corresponding aldehydes/ketones with hydroxylamine. With theadvances in organometallic chemistry, free-radical chemistry and other syntheticapproaches, almost any kind of oximes bearing a variety of functional groups could beachieved nowadays.The application of oximes has received much attention for decades. Some oximederivatives are known today as agricultural chemicals, either herbicides or pesticides,while others are used as antidote and anti-infection agents, and as excellent ligands intransition-metal -catalyzed reactions.Oximes have emerged as versatile synthetic intermediates in organic chemistryowing to their ready accessibility and active structural feature. In general, theirreactions are focused on Beckmann rearrangement, deoximation, reduction, oxidation,1,3-dipolar cycloaddition and dehydration.As a structure-special class of oximes,α-ethylidene-β-oxo oximes were easy toundergo ring-opening and intramolecular aza-cyclization according to our reportedexperimental results. As a continuation of previous work, this thesis mainyl includetwo aspects concerning their reactivity towards different dehydration agents.1. Under Appel conditions, a series of highly substituted isoxazoles weresynthesized in high yields fromα-ethylidene-β-oxo oximes via a ring-opening andintramolecular cyclization process. A plausible mechanism is also proposed.2. By treatment ofα-ethylidene-β-oxo oximes with TsCl/KOH, spiro-fusedpyrazolin-5-ones were obtained via tandem ketoxime tosylation and intramolecularcyclization.In summary, efficient and divergent synthesis of fully substituted isoxazoles andspiro-fused pyrazolin-5-ones is developed fromα-ethylidene-β-oxo oximes based onselection of dehydration agents. This protocol is associated with readily availablestarting materials, mild conditions, dense and flexible substitution patterns, importantsynthetic potential of the final products, and easy control of the reaction orientation byreaction conditions selection.

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CLC: > Mathematical sciences and chemical > Chemistry > Organic Chemistry > Organic Chemistry general issues > Properties of organic compounds > Chemical properties of organic reactions
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