Formal Enantioselective [4+3] Cycloaddition by a Tandem Diels–Alder Reaction/Ring Expansion

Abstract

The tandem Diels-Alder reaction/ring expansion between cyclopentadiene and unsaturated aldehydes is a highly stereoselective process for the synthesis of bicycloA C H T U N G T R E N N U N G [3.2.1]octenones, the formal products of a [4 + 3] cycloaddition. When the initial cycloaddition was conducted in the presence of the chiral Lewis acid catalyst 14, the bicycloA C H T U N G T R E N N U N G [3.2.1]octenones were obtained in two steps in 72-85 % yields with up to 96 % ee and > 98 % de.

Sequential Diels–Alder Reaction/Rearrangement Sequence: Synthesis of Functionalized Bicyclo[2.2.1]heptane Derivatives and Revision of Their Relative Configuration

“…The combination of Diels–Alder (DA) cycloaddition reactions with other transformations without isolating the intermediates allows a very rapid increase in the complexity of products. − For example, Lewis acid promoted rearrangements of DA products have been reported recently. − Davies and Dai showed that DA addition of alkylated acroleins with cyclopentadiene affords the formal [4 + 3] rather than the kinetic [4 + 2] cycloadducts under appropriate Lewis acid catalysis. , The reaction sequence comprises a domino DA and two consecutive 1,2-shifts, delivering bicyclo[3.2.1]­oct-6-en-3-ones 4 (Scheme , eq A). The rearrangement proved to be stereoselective with retained enantioselectivity introduced during the DA step . In contrast, α-oxy-substituted acroleins 5 and 9 were believed to undergo concerted [4 + 3] cycloadditions of allyl cations with both cyclic and acyclic dienes (Scheme , eqs B and C). − …”

(4+3) Cycloaddition Reactions of Nitrogen‐Stabilized Oxyallyl Cations

“…Surprisingly, there have only been two reports of catalytic asymmetric (4+3) cycloadditions31 using nitrogen‐stabilized oxyallyl cations, but the potential for future development in this area is promising and merits further exploration.…”

A Tandem 1,3-H-Shift–6π-Electrocyclization–Cyclic 2-Amido-diene Intramolecular Diels–Alder Cycloaddition Approach to BCD-Ring of Atropurpuran

“…Consequently, we turned our attention to chiral allenamide 31 -Bn, which was synthesized from enal 28 23 [ Scheme 5 ]. It was quickly evident that each of these internally tethered systems behaves quite differently.…”