The acyl nitroso Diels–Alder reaction of 1,3‐dienes with electrochemically oxidised hydroxamic acids is described. By using alternating current electrolysis, their typical electro‐induced decomposition could be suppressed in favour of the 1,2‐oxazine cycloaddition products. The reaction was optimised using Design of Experiments (DoE) and a sensitivity test was conducted. A mixture of triethylamine/hexafluoroisopropanol served as supporting electrolyte in dichloromethane, thus giving products of high purity after evaporation of the volatiles without further purification. The optimised reaction conditions were applied to various 1,3‐dienes and hydroxamic acids, giving up to 96 % isolated yield.
An electrochemical synthesis of organic polysulfides through sulfur insertion from elemental sulfur to disulfides or thiols is introduced. The highly economic, low-sensitive and low-priced reaction gives a mixture of polysulfides, whose distribution can be influenced by the addition of different amounts of carbon disulfide as co-solvent. To describe the variable distribution function of the polysulfides, a novel parameter, the "absorbance average sulfur amount in poly-sulfides" (SAP) was introduced and defined on the basis of the "number average molar mass" used in polymer chemistry. Various organic polysulfides were synthesized with variable volume fractions of carbon disulfide, and the yield of each polysulfide was determined by quantitative 13 C NMR. Moreover, by using two symmetrical disulfides or a disulfide and a thiol as starting materials, a mixture of symmetrical and asymmetrical polysulfides could be obtained.
Beschrieben wird die Acyl-Nitroso Diels-Alder-Reaktion von 1,3-Dienen mit elektrochemisch oxidierten Hydroxamsäuren. Durch die Verwendung von Wechselstrom konnte ihr elektro-induzierter Zerfall zugunsten der 1,2-Oxazin-Cycloadditionsprodukte unterdrückt werden. Die Reaktion wurde mittels statistischer Versuchsplanung (Design of Experiment, DoE) optimiert und durch einen Sensitivitätstest weiter untersucht. Ein Gemisch aus Triethylamin und Hexafluorisopropanol dient als Leitsalz in Dichlormethan, wodurch hochreine Produkte nach Verdampfen der flüchtigen Komponenten gewonnen werden kçnnen. Mit den optimierten Bedingungen wurden verschiedene 1,3-Diene und Hydroxamsäuren umgesetzt, deren Produkte in bis zu 96 % Ausbeute isoliert wurden.
1,2-Oxazines were synthesised via a copper-catalysed aerobic acyl nitroso Diels-Alder reaction from 1,4-disubstituted 1,3-dienes and N-Boc-hydroxylamine. From this, 1,2-oxazinanes were received in a novel follow-up reaction path. The stability of several 1,2-oxazines and 1,2-oxazinanes towards organometallic compounds was tested to rate their operability as cyclic chiral Weinreb amide auxiliaries. 3,6-Di-tert-butyl-1,2-oxazinane gave the best results and was introduced as chiral Weinreb amide-type auxiliary to yield chiral α-substituted ketones in a diastereomeric ratio of up to 98:2. The removal of the auxiliary can be performed with BuLi to form unsymmetrical α-chiral ketones. Thereafter, the chiral auxiliary can be re-isolated and purified by sublimation in vacuum.
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