Hydrogen Bond-Assisted 6π-Azaelectrocyclization of Penta-2,4-dienamides: Synthesis of Dihydropyridin-2(3H)-ones

Abstract

A facile and efficient synthesis of substituted dihydropyridin-2(3H)-ones is developed from penta-2,4-dienamides, in which an intramolecular C-N bond was formed through thermal 6π-azaelectrocyclization. The intramolecular hydrogen bonding-assisted cyclization reaction opens access to a variety of dihydropyridin-2(3H)-ones.

CuO/I2-mediated intramolecular annulation for the synthesis of 2-aroyl-3-hydroxy-4-iodonaphthalenes

“…The prefabricated substrate 1m was also subjected to the reaction under the standard conditions, however, we could not obtain the corresponding product 2m (Scheme 2c), which indirectly indicated that the two carbanyl groups in substrate 1 were extremely necessary in the transformation of the hydrogen bond-assisted 6π-electrocyclization. Although mechanistic details are not clear at this stage, on the basis of these experimental results and previous reports from the literature, 16,18,19 a possible reaction mechanism was proposed in Scheme 3 using (Z)-2-phenylidene-1-phenylbutane-1,3-dione (1a) as an example. The reaction would begin with the copper(II) oxidepromoted iodination of the methyl ketone group in 1a to afford intermediate B, 16 which would be subsequently converted to intermediate C via iodine-catalyzed cis/trans-isomerization of its carbon-carbon double bond.…”

Resonance‐Assisted Hydrogen Bonding as a Driving Force in Synthesis and a Synthon in the Design of Materials

“…[146] The simple performance, readily available substrates, good yields, and synthetic potential of the products make this method highly desirable. [146] The simple performance, readily available substrates, good yields, and synthetic potential of the products make this method highly desirable.…”

“…The RAHB‐assisted thermal 6 π‐aza‐electrocyclization of penta‐2,4‐dienamides led to formation of an intramolecular C−N bond and a β‐diketone moiety in the efficient synthesis of substituted dihydropyridin‐2(3 H )‐ones (Scheme ) . The simple performance, readily available substrates, good yields, and synthetic potential of the products make this method highly desirable.…”

H‐Bond: Τhe Chemistry‐Biology H‐Bridge

“…The stability of the intramolecular H‐bond is attributed to resonance assistance giving extended π‐delocalization. In this context, the impact of intramolecular H‐bonding on substituent properties or intramolecular cyclizations has been investigated …”