Organocatalyzed Oxa-Diels–Alder Reactions: Recent Progress

Abstract

Oxa-Diels-Alder reaction is a straightforward, atom-economical process for the construction of six membered oxa-cycle which is a privileged structure due to its omnipresence in several pharmaceuticals and natural products. Like many other asymmetric transformations, organocatalysis provides an elegant pathway to their synthesis via [4+2] annulation under mild reaction conditions. The oxa-Diels reactions either utilize α,β-unsaturated carbonyl as oxadiene with a suitable dienophile or simple carbonyl as dienophile with other dienes. A range of organocatalysts have been explored in the past decade to execute this strategy. The catalysts induce stereoselectivities via two basic reactivities: 1) Formation of chiral intermediates, 2) Selectively activating suitable reactants in transition state. The present review assembles organocatalyzed asymmetric oxa-Diels-Alder reactions published in last ten years’ time span with detailed discussion on mechanistic approaches.

Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

“…This is a very large group of reactions which may be the first coming to mind when talking about organocatalysis in general. Examples of typical reaction types for redox-neutral asymmetric organocatalysis are aldol reactions [13], Michael reactions [14][15][16], and Diels-Alder reactions [17,18].…”

Diastereodivergent Asymmetric [4 + 2] Cycloaddition of In Situ Generated ortho-Quinone Methides and Allenyl Ketones Enabled by Chiral Phosphoric Acid Catalysis

“…Consequently, the synthesis of chromanes, particularly the enantioselective synthesis of chiral chromanes, has attracted considerable research interest among chemists . Despite the development of various strategies for the catalytic asymmetric synthesis of chromanes, the enantioselective inverse-electron-demand oxa-Diels–Alder reaction between ortho -quinone methides ( o -QMs), either stable or in situ-generated, and electron-rich olefins represents the most straightforward and efficient protocol . Since the first asymmetric [4 + 2] cycloadditions of β-diketones with the o -QM generated in situ from ortho -hydroxybenzyl alcohols using chiral phosphoric acid (CPA) catalysts by Schneider and co-workers, this strategy has been expanded to encompass various 2π-components, including enamides, enol precursors, vinyl sulfides, vinylindoles, vinylnaphthols, and even the unactivated alkenes (Figure , a).…”

Synthesis of azepane-fused pyrano[3,2-b]indoles by Lewis acid-catalysed oxa Diels–Alder reactions

“…7 The oxa Diels-Alder ('ODA') reaction is one among the most efficient methods for the synthesis of functionalized pyran derivatives, as it allows for the stereoselective construction of this key motif in a single step. 8 Here, we report the synthesis of novel polycyclic pyrano [3,2-b]indoles fused with an azepane ring, by way of the Lewis acid-catalysed ODA reaction between enol ethers and unsaturated azepino[1,2-a]indole dione derivatives (Scheme 1b). The latter enone components for the oxa [4 + 2] cycloaddition are readily accessible through a sensitized catalytic cascade photooxygenation of cyclohepta [b]indoles previously developed in our laboratory, 9 followed by dehydration.…”