Nitrogen-Stabilized Oxyallyl Cations Research Articles

ChemInform Abstract: An Approach to Cyclohepta[b]indoles Through an Allenamide [4 + 3] Cycloaddition—Grignard Cyclization—Chugaev Elimination Sequence.

A strategy for synthesizing highly functionalized cyclohepta[b]indoles through a concise (4 + 3) cycloaddition–cyclization–elimination sequence is described. The cycloaddition features nitrogen-stabilized oxyallyl cations derived from epoxidations of N-aryl-N-sulfonyl-substituted allenamides, while the cyclization and elimination employed an intramolecular Grignard addition and a one-step Chugaev process, respectively.

An approach to cyclohepta[b]indoles through an allenamide (4 + 3) cycloaddition-Grignard cyclization-Chugaev elimination sequence.

A strategy for synthesizing highly functionalized cyclohepta[b]indoles through a concise (4 + 3) cycloaddition–cyclization–elimination sequence is described. The cycloaddition features nitrogen-stabilized oxyallyl cations derived from epoxidations of N-aryl-N-sulfonyl-substituted allenamides, while the cyclization and elimination employed an intramolecular Grignard addition and a one-step Chugaev process, respectively.

ChemInform Abstract: [4 + 3] Cycloaddition Reactions of Nitrogen‐Stabilized Oxyallyl Cations

AbstractReview: 75 refs.

Developing a diastereoselective intramolecular [4+3] cycloaddition of nitrogen-stabilized oxyallyl cations derived from N-sulfonyl-substituted allenamides.

Efforts toward achieving a practical and diastereoselective intramolecular [4+3] cycloaddition of nitrogen-stabilized oxyallyl cations with tethered dienes are described. Epoxidation of N-sulfonyl substituted allenamides with dimethyldioxirane (DMDO) generates nitrogen-stabilized oxyallyl cations that readily undergo stereoselective [4+3] cycloaddition with dienes. Selectivity is found to depend on the tethering length as well as the stability of the oxyallyl cation intermediate, whether generated from N-carbamoyl- or N-sulfonyl-substituted allenamides. The use of chiral N-sulfonyl-substituted allenamides provided minimal diastereoselectivity in the cycloaddition, while high diastereoselectivity can be achieved with a stereocenter present on the tether. These studies provide further support for the synthetic utility of allenamides.

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

The use of heteroatom-substituted oxyallyl cations in (4+3) cycloadditions has had a tremendous impact on the development of cycloaddition chemistry. Extensive efforts have been exerted toward investigating the effect of oxygen, sulfur, and halogen substituents on the reactivity of oxyallyl cations. Most recently, the use of nitrogen-stabilized oxyallyl cations has gained prominence in the area of (4+3) cycloadditions. The following article will provide an overview of this concept utilizing nitrogen-stabilized oxyallyl cations.

An Unexpected Reversal of Diastereoselectivity in the [4+3]-Cycloaddition Reaction of Nitrogen-Stabilized Oxyallyl Cations with Methyl 2-Furoate

An unexpected reversal of diastereoselectivity in the [4+3] cycloaddition of methyl 2-fuorate with nitrogen-stabilized oxyallyl cations derived from epoxidation of chiral allenamides is described here. This intriguing reversal in favor of the endo-II cycloaddition pathway is likely a result of minimizing the dipole interaction between the oxyallyl cation and ester carbonyl of methyl 2-fuorate.

Highly Stereoselective [4 + 3] Cycloadditions of Nitrogen-Stabilized Oxyallyl Cations with Pyrroles. An Approach to Parvineostemonine

[structure: see text]. A highly stereoselective [4 + 3] cycloaddition of N-substituted pyrroles with allenamide-derived nitrogen-stabilized chiral oxyallyl cations is described here. This method provides an approach for constructing tropinone alkaloids.

Chiral Lewis Acid-Catalyzed Highly Enantioselective [4 + 3] Cycloaddition Reactions of Nitrogen-Stabilized Oxyallyl Cations Derived from Allenamides

A chiral Lewis acid-catalyzed highly enantioselective [4 + 3] cycloaddition reaction of allenamide-derived nitrogen-stabilized chiral oxyallyl cations is described here. The use of bisoxazoline ligand and CuOTf2 provides high enantioselectivity, especially with [SbF6]- as the counteranion.

Chiral Enamide. Part 1. Epoxidations of Chiral Enamides. A Viable Approach to Chiral Nitrogen‐Stabilized Oxyallyl Cations in [4 + 3] Cycloadditions.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Chiral enamide. Part 1: Epoxidations of chiral enamides. A viable approach to chiral nitrogen stabilized oxyallyl cations in [4+3] cycloadditions

The first study of stereoselective epoxidations of chiral enamides is described here. Its potential in the synthesis of chiral α-keto aminals as a viable approach to nitrogen stabilized oxyallyl cations in stereoselective [4+3] cycloadditions is also illustrated.