Chloranil as an Efficient Oxidant of the Cyclohexadiene Intermediates Formed by a Cycloaddition of Substituted 2H‐Pyran‐2‐ones and Styrenes En Route to the Boscalid Derivatives

Abstract

We describe a three‐step one‐pot metal‐free domino procedure yielding a set of boscalid derivatives, parent compound being a highly important agrochemical agent. The first step of the process consists of the Diels–Alder reaction between a substituted 2H‐pyran‐2‐one and styrene derivatives, followed by the elimination of CO2 and aromatization (oxidation). The last step was found to be efficiently promoted by the application of chloranil as the oxidant. Alternatively, activated carbon Darco KB could also act as the dehydrogenation catalyst necessitating a larger excess of the styrene to act as the hydrogen acceptor.

Diels-Alder reactions of 1-amino-1,3-dienes and related systems

“…Amino-2H-pyran-2-ones also behave as electron-rich cyclic 1-aminodienes in DA reactions. The preparation and DA reactions of α-amino-2H-pyran-2-ones have been studied by Kočevar's group extensively [170][171][172][173][174][175][176][177][178][179][180][181][182][183]. Fused 2H-pyran-2-ones 294 reacted with maleimides in boiling decalin during ca.…”

“…When the cycloaddition of pyranones 299 was carried out with styrenes in the presence of chloranil as oxidant under MW irradiation or activated carbon as dehydrogenation catalyst under conventional heating the corresponding boscalid derivatives 303 were obtained (Scheme 74) [181,182]. Styrenes acted as synthetic equivalents of phenylacetylenes in this method for the synthesis of derivatives of the fungicide boscalid.…”

A 26-Membered Macrocycle Obtained by a Double Diels–Alder Cycloaddition Between Two 2H-Pyran-2-one Rings and Two 1,1'-(Hexane-1,6-diyl)bis (1H-pyrrole-2,5-dione)s

“…[27][28][29][30][31] Namely, it was already observed that 2H-pyran-2-ones can act as "double" dienes, reacting in two consecutive Diels-Alder reactions with two distinctive molecules of the dienophiles, yielding bicyclo[2.2.2]octenes. 30 The initial cycloaddition step leads to the formation of CO 2 -bridged oxabicyclo[2.2.2]octenes that in the next step eliminate a molecule of CO 2 (via a retro-hetero-Diels-Alder reaction) providing cyclohexadiene systems that act as new dienes for another molecule of dienophile finally providing the double cycloadducts.…”

Synthesis and Structural Evaluation of 5-Methyl-6-acetyl Substituted Indole and Gramine

“…[16][17][18][19][20][21] Here we applied (Z)-1-methoxybut-1-en-3-yne (4) as the dienophile cycloadding on 2H-pyran-2-one derivative 3 yielding a crucial intermediate 5, a substituted N-{2-[(Z)-2-methoxyethenyl]phenyl}benzamide (Scheme 1). This intermediate 5 has a strategically positioned methoxy group bound to the ethenyl fragment being in an ortho position to the benzamido group, therefore enabling a straightforward cyclization towards the indole ring (i.e.…”