Assessment on facile Diels–Alder approach of α-pyrone and terpenoquinone for the expedient synthesis of various natural scaffolds

Abstract

The development of highly facile synthetic procedures for the expedient synthesis of complex natural molecules is always in demand. As this aspect, the Diels–Alder reaction (DAR) has a versatile approach to the synthesis of complex natural compounds and highly regio-/stereoselcetive heterocyclic scaffolds. Additionally, α-pyrone and terpenoquinone are two versatile key intermediates that are prevalent in various bioactive natural compounds for instance, (±)-crinine, (±)-joubertinamine, (±)-pancratistatin, (−)-cyclozonarone, and 8-ephipuupehedione, etc. Hence, the current review summarizes the Diels–Alder reaction application of α-pyrone and terpenoquinone to the constructive synthesis of various natural products over the past two decades (2001–2021). Equally, it serves as a stencil for the invention and development of new synthetic strategies for high-complex molecular structured natural and heterocyclic molecules. Graphical Abstract

Access to functionalized 2-pyrones through cascade reactions of α-halothioesters involving DBU-derived ammonium ylides

“…1 Additionally, 2-pyrones can also serve as versatile synthons in organic synthesis (Scheme 1b). 2 Due to the biological and synthetic utility of 2-pyrones, much effort has been directed toward the preparation of diversely functionalized 2-pyrones and many sophisticated works have been reported. 3 For example, Smith 3 e developed a one-pot isothiourea-mediated Michael addition/lactonization/thiol elimination cascade sequence from (phenylthio)acetic acids and α,β-unsaturated trifluoromethyl ketones to produce trifluoromethyl-substituted 2-pyrones (Scheme 2a).…”

Resolution by diastereomeric salts: Access to both enantiomers of racemic acid using the same enantiomer of resolving base

“…The acid 1 is readily available by a Diels‐Alder reaction between corresponding α‐pyrone and acrylate dienophile. That kind of compounds are valuable intermediates for the synthesis of a number of natural products 2 . Diels‐Alder chemistry applied to α‐pyrones allowed to construct a bicyclolactone backbone of syntactically challenging metabolites such as basiliolides, 3 transtaganolides, 3,4 or scholarisine 5 .…”

“…Diels‐Alder chemistry applied to α‐pyrones allowed to construct a bicyclolactone backbone of syntactically challenging metabolites such as basiliolides, 3 transtaganolides, 3,4 or scholarisine 5 . Furthermore, bicyclic compounds can serve as a source of functionalized cyclohexenes due to the cleavable lactone bond 1,2 . The advantage of this approach is a control of the relative stereochemistry of several simultaneously formed chiral centers in a Diels‐Alder adduct.…”

“…That kind of compounds are valuable intermediates for the synthesis of a number of natural products. 2 Diels-Alder chemistry applied to α-pyrones allowed to construct a bicyclolactone backbone of syntactically challenging metabolites such as basiliolides, 3 transtaganolides, 3,4 or scholarisine. 5 Furthermore, bicyclic compounds can serve as a source of functionalized cyclohexenes due to the cleavable lactone bond.…”

Oxidant free synthesis of α-pyronesviaan NHC-catalyzed [3 + 3] annulation of bromoenals with 2-chloro-1,3-diketones

“…α-Pyrones are important structural motifs that exist in numerous bioactive natural products and medicines. 1 For example, nigerapyrone and salinipyrone A containing α-pyrone fragments are used in the clinical treatment of multiple cancers. 2 Albidopyrone, a new α-pyrone moiety, has been found to have inhibitory activity against protein-tyrosine phosphatase B.…”