3-oxidopyrylium Betaine Research Articles

Cycloaddition profile of pentafulvenes with 3-oxidopyrylium betaine: experimental and theoretical investigations

A detailed investigation on the effect of solvent polarity, temperature, and microwave irradiation on periselectivity in cycloaddition reactions of pentafulvenes with 3-oxidopyrylium betaine is described. The base catalyzed generation of 3-oxidopyrylium betaine in CHCl3 resulted in the exclusive formation of [6+3] adducts. With increase in solvent polarity and temperature, mixtures of [6+3] and [3+2] adducts were formed, where as under microwave irradiation, [3+2] adducts were formed exclusively. The experimental results have been rationalized on the basis of theoretical calculations.

Periselectivity in the Cycloaddition Reactions of Pentafulvenes with 3-Oxidopyrylium Betaines: Effect of Substituent on the C-6 Carbon

Periselectvity in cycloaddition reactions of pentafulvenes with 3-oxidopyrylium betaines is examined. The results of our studies show that depending on the substituent on the C-6 carbon, the reaction may proceed either through the [6+3] or the [3+2] pathway. The results of our investigations with various pentafulvenes are discussed.

Dipolar Cycloaddition of Dicyclopentadiene with 3-Oxidopyrylium Betaine: An Entry into Methano-Bridged 5-6-7-Fused Ring System

The [3+2] cycloaddition of 3-oxidopyrylium ylide, generated from an acetoxypyranone, proceeds with complete chemo- and stereoselectivity. The approach of the dipole takes place exclusively from the EXO-face of the bicycloheptane moiety providing a mixture of regioisomers in approximately 55:45 ratio. The derived cycloadduct is then transformed to a novel SYN- ANTI- CIS-condensed methano-bridged molecular entity.

A Practical Approach to Stereochemically Defined Tetrahydrofurans from [5+2] Oxidopyrylium-Alkene Cycloadducts

The feasibility of the Beckmann fragmentation reaction has been extended to [5+2] cycloadducts derived from the cycloaddition of 3-oxidopyrylium betaine to various olefins. Upon cleavage, these cycloadducts give stereochemically defined tetrahydrofurans in high overall yields as single diastereoisomers.

Studies on the synthetic utility of [6+3] cycloaddition of pentafulvenes with 3-oxidopyrylium betaines: efficient synthesis of fused ring cyclooctanoids

A study on the synthetic utility of [6+3] cycloaddition of pentafulvenes with 3-oxidopyrylium betaines is described. 5–8 Fused oxa-bridged cyclooctanoids, the products of the above methodology undergo facile Diels–Alder reaction, dipolar cycloaddition, Luche reduction and selective hydrogenation over Pd/C leading to functionalized molecules, which can be transformed to oxa-bridged fused cyclooctanoids. We have shown that the carbon framework of the molecules can be directly expanded from the product, thus enhancing the synthetic versatility of the products.

6 + 3] Cycloaddition of Pentafulvenes with 3‐Oxidopyrylium Betaine: A Novel Methodology Toward the Synthesis of 5—8 Fused Oxabridged Cyclooctanoids.

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6+3] Cycloaddition of pentafulvenes with 3-oxidopyrylium betaine: a novel methodology toward the synthesis of 5–8 fused oxabridged cyclooctanoids

Abstract Pentafulvenes undergo a facile [6+3] cycloaddition with 3-oxidopyrylium betaine, generated from the corresponding pyranulose acetate, leading to the formation of 5–8 fused oxabridged cyclooctanoids. The product is formed by a [6+3] cycloaddition, followed by a 1,5-hydrogen shift of the initially formed [6+3] adduct. The reaction was found to be general and a number of fulvenes with a wide range of substituents at the exocyclic double bond, that is, at the C6 position followed a similar reactivity pattern. The [6+3] adduct, a 5–8 fused oxabridged cyclooctanoid, is potentially amenable to a number of synthetic transformations due to the presence of an α,β-unsaturated ketone and cyclopentadiene part. By selecting appropriately substituted fulvene and pyranulose acetates, it is possible to use this methodology for the synthesis of a wide range of 5–8 fused cyclooctanoids. The experimental results have been rationalized on the basis of theoretical calculations.

Regioselective Synthesis of Novel 7-5-8-Fused Oxabridged Tricyclic Molecules via Consecutive Dipolar Cycloaddition of Pentafulvenes with 3-Oxidopyrylium Betaines

Pentafulvenes undergo consecutive dipolar cycloadditions with various substituted oxidopyrylium betaines resulting in the formation of a new class of structurally interesting 7-5-8-fused oxabridged tricyclic molecules.

6 + 3] Cycloaddition of Fulvenes with 3‐Oxidopyrylium Betaine: A Novel Methodology for the Synthesis of Fused Cyclooctanoid Natural Products.

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6+3] Cycloaddition of fulvenes with 3-oxidopyrylium betaine: a novel methodology for the synthesis of fused cyclooctanoid natural products

Fulvenes undergo an easy [6+3] cycloaddition with 3-oxidopyrylium betaines leading to 5–8 fused oxabridged cyclooctanoids.

Highly diastereoselective 1,3-dipolar cycloaddition reactions of trans-2-methylene-1,3-dithiolane 1,3-dioxide with 3-oxidopyridinium and 3-oxidopyrylium betaines: a route to the tropane skeleton.

The C2-symmetric vinyl sulfoxide, trans-2-methylene-1,3-dithiolane 1,3-dioxide, was found to react with a range of 3-oxidopyridinium betaines (bearing different substituents on nitrogen) in high yield and with total diastereoselectivity. A 2.3:1 mixture of regioisomers was formed with all of the 3-oxidopyridinium betaines but the ratio was found to change over prolonged periods of time due to reversibility of the minor regioisomer. 3-Oxidopyridinium betaines bearing methyl substituents at either the 2- or 6-position were also tested in the cycloaddition process. Improved regioselectivity (8:1) and again high diastereoselectivity were observed with the betaine having an additional substituent at the 2-position, but with betaines having a substituent in the 6-position although high regioselectivity was observed (9.9:1), the major isomer was formed with low diastereoselectivity (5.5:4.4). The origin of the regio- and diastereo-selectivity with all the betaines is discussed. Finally, the C2-symmetric vinyl sulfoxide, trans-2-methylene-1,3-dithiolane 1,3-dioxide was reacted with an oxidopyrylium betaine in moderate yield. Good regioselectivity and moderate diastereoselectivity were observed.