Facile synthesis of 2,4‐dienals via an arsonium salt and its application to some natural products

Abstract

Therefore, methodology for synthesizing dienals has attracted the attention of synthetic organic chemists. The methods reported in the literature use LiCH=CH-CH=CHOEt[2] or CH3COCH =CHSCMe3 [3] with aldehyde, but both of these suffer from difficulty in obtaining the reagents or from the need for multiple-step reactions to afford the desired dienal. Alternatively, a Wittig reagent, Ph3P=CHCH=CHCH0, has been used [4]. Its application to the synthesis of leukotriene has appeared in the literature [5]. A roundabout procedure to achieve formylenylolefination has been used, for example, in the synthesis of Wallemia A [61.Wallemia A In extension of our previously reported formylolefination via an arsonium salt [7] we would like to report here a facile formylenylolefination via the arsonium salt, formylallyltriphenylarsonium bromide (2), and its application in the syntheses of navenone A [8] and Otanthus maritima amide [9].

Occurrence of an Elongated p-Oxo Ketene Intermediate in the Dissociative Alkaline Hydrolysis of Aryl (2E,4E)-5-(4‘-Hydroxyphenyl)pentadienoates

“…The acids were obtained through a Wittig-type reaction under phase-transfer conditions from 4-hydroxybenzaldehyde (protected with the tert -butyldimethylsilyl group) 14 or 4-methoxybenzaldehyde, and 3-ethoxycarbonylallylidenetriphenylarsonium bromide, prepared from triphenylarsine and commercial (Aldrich) ethyl 4-bromocrotonate as described . These reactions furnished, in good yield, nearly a 4:1 mixture of the E,E / E,Z isomers, as previously reported, and confirmed by 1 H NMR spectroscopy (the stereoisomers have well-resolved spectra in acetone- d 6 , and the peak assignments and the attribution of the configurations have been conveniently carried out by a simple decoupling technique) but our attempts to obtain total conversion of the mixture of isomers into the E,E isomer by treatment with iodine in daylight 5,13 failed. The mixtures of isomers were subsequently hydrolyzed in aqueous sodium hydroxide (10%) at reflux overnight.…”

Mechanism of Alkaline Hydrolysis of Some HO-π-COOAr Acyl Derivatives

“…After condensation with 2,4-dinitrophenol in the presence of dicyclohexylcarbodiimide, the usual workup of the reaction afforded again a mixture of the E / Z isomers of the desired ester as shown by the 1 H NMR spectrum. Finally, the cis isomer was easily and completely converted into the trans isomer simply by treating a solution of the mixture of isomers in dichloromethane with a catalytic amount of iodine in daylight for a few hours …”

Triphenylarsine

“…The latter can be isomerized to the former by treating with a catalytic amount of Iodine in daylight (eq 5) 9. …”