Diastereoselective and Regioselective Singlet-Oxygen Ene Reaction of Oxazolidine-Substituted Alkenes:  Control through Hydrogen Bonding Mediated by the Urea Functionality of Chiral Auxiliaries

Adam, Waldemar; Peters, Karl; Peters, ‡ and Eva-Maria; Schambony, Simon B.

doi:10.1021/ja001113l

Cited by 34 publications

(15 citation statements)

References 22 publications

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“…It should be emphasized that the configuration at the C3 position of the enecarbamate does not influence the diastereoselectivity, since the same diastereomer is obtained irrespective of whether the (3R)-or (3S)-configured encarbamates 2c(3R) and 2c-(3S) (entries 3 and 4, Table 1) are employed. Furthermore, the photooxygenation of enecarbamate 2c(3R) in CD 3 OD:CDCl 3 (4.1: 1) and in CD 3 COCD 3 :CDCl 3 (2.4:1) solvent mixtures (entries 6 and 7, Table 1) resulted in the same selectivity as in CDCl 3 . Therefore, the diastereomeric ratio also does not depend on the solvent polarity, which suggests that the carbonyl group plays no significant role in the stereochemical outcome of this [2 + 2] cycloaddition.…”

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confidence: 85%

“…Recently we have also discovered the diastereoselective ene reaction of 1 O 2 with optically active oxazolidines, which have been equipped with an urea functionality. 3 The diastereoselective control was achieved in this ene reaction through remote hydrogen bonding between the urea NH bond and 1 O 2 , whereas steric factors were held responsible in the [4 + 2] cycloaddition. Similar efficacious hydrogen-bonding effects have been documented 4 for the [2 + 2] cycloadditions of 1 O 2 with chiral allylic alcohols.…”

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confidence: 99%

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A Highly Diastereoselective Dioxetane Formation by the Hydroxy-Directed [2+2] Cycloaddition of Singlet Oxygen to a Chiral Allylic Alcohol

1999

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Chiral auxiliaries have been successfully employed in controlling the diastereoselectivity of numerous reactions. 1 A notoriously difficult problem is the manipulation of the stereochemical course of singlet oxygen ( 1 O 2 ), the smallest possible cyclophile. In the past few years, we have shown that through the appropriate choice of the chiral inductor it is possible to control the stereoselectivity of the [4 + 2] cycloaddition of 1 O 2 . 2 For this purpose, optically active 2,2-dimethyloxazolidines proved to be highly effective chiral auxiliaries when attached to sorbic acid in the form of an amide linkage. Recently we have also discovered the diastereoselective ene reaction of 1 O 2 with optically active oxazolidines, which have been equipped with an urea functionality. 3 The diastereoselective control was achieved in this ene reaction through remote hydrogen bonding between the urea NH bond and 1 O 2 , whereas steric factors were held responsible in the [4 + 2] cycloaddition. Similar efficacious hydrogen-bonding effects have been documented 4 for the [2 + 2] cycloadditions of 1 O 2 with chiral allylic alcohols. To date, no cases appear to be known in which steric interactions efficiently guide the π-facial attack of 1 O 2 in the dioxetane formation; however, the stereoselective dioxetane formation in the ozonolysis of vinylsilanes has been reported. 5 Herein we report the first example of a chiral-auxiliary-induced [2 + 2] cycloaddition between 1 O 2 and oxazolidinone-functionalized enecarbamates, which proceeds with complete diastereoselectivity as a result of steric repulsions.Evans' chiral auxiliary 6 was introduced into the enecarbamate substrate 2 by condensing the 4-alkyl-substituted oxazolidinones with the aldehyde

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confidence: 85%

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A Highly Diastereoselective Dioxetane Formation by the Hydroxy-Directed [2+2] Cycloaddition of Singlet Oxygen to a Chiral Allylic Alcohol

1999

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“…The photooxygenation of oxazolidines 7a – d through the formation of hydroperoxides 8a–d gives spiro-fused oxazolidine-containing dioxolanes 9a–d in low yields (12–30%) ( Scheme 3 ) [ 233 ].…”

Section: Reviewmentioning

confidence: 99%

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

Terent’ev¹,

Borisov²,

Vil³

et al. 2014

Beilstein J. Org. Chem.

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SummaryThe present review describes the current status of synthetic five and six-membered cyclic peroxides such as 1,2-dioxolanes, 1,2,4-trioxolanes (ozonides), 1,2-dioxanes, 1,2-dioxenes, 1,2,4-trioxanes, and 1,2,4,5-tetraoxanes. The literature from 2000 onwards is surveyed to provide an update on synthesis of cyclic peroxides. The indicated period of time is, on the whole, characterized by the development of new efficient and scale-up methods for the preparation of these cyclic compounds. It was shown that cyclic peroxides remain unchanged throughout the course of a wide range of fundamental organic reactions. Due to these properties, the molecular structures can be greatly modified to give peroxide ring-retaining products. The chemistry of cyclic peroxides has attracted considerable attention, because these compounds are used in medicine for the design of antimalarial, antihelminthic, and antitumor agents.

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“…217 Another recent example for the use of oxazolidine auxiliaries is the asymmetric epoxidation of acetylated or carbamoyl-substituted oxazolidines 205 reported by Schambony and co-workers. 218,219 A hydrogen bond between the urea functionality NH and the oxidant seems to be important for high stereoselectivities. This can be deduced from a reversal in stereoselectivity in the case where the substrate with R 4 = Me is employed (26:74 dr).…”

Section: Oxazolidinesmentioning

confidence: 99%

Chiral Auxiliaries - Principles and Recent Applications

Gnas¹,

Glorius²

2006

Synthesis

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With modern methods for asymmetric catalysis breaking ground, the use of chiral auxiliaries seems to be old-fashioned and rather inefficient. However, for many transformations, chiral auxiliaries often represent the only selective method available. In addition, high levels of selectivity and reliability are often attractive characteristics of chiral auxiliaries and allow for the efficient and rapid synthesis of desired chiral compounds. In addition, even in cases with imperfect selectivity, the use of an attached chiral auxiliary allows the enrichment of diastereoselectivity, and hence enantioselectivity after removal of the auxiliary, by many standard separation techniques. This article gives an overview on the most important classes of chiral auxiliaries, discussing the mode of action and highlighting some recent applications. It does not deal with the use of chiral catalysts, chiral reagents or achiral auxiliaries.

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Diastereoselective and Regioselective Singlet-Oxygen Ene Reaction of Oxazolidine-Substituted Alkenes: Control through Hydrogen Bonding Mediated by the Urea Functionality of Chiral Auxiliaries

Cited by 34 publications

References 22 publications

A Highly Diastereoselective Dioxetane Formation by the Hydroxy-Directed [2+2] Cycloaddition of Singlet Oxygen to a Chiral Allylic Alcohol

A Highly Diastereoselective Dioxetane Formation by the Hydroxy-Directed [2+2] Cycloaddition of Singlet Oxygen to a Chiral Allylic Alcohol

Synthesis of five- and six-membered cyclic organic peroxides: Key transformations into peroxide ring-retaining products

Chiral Auxiliaries - Principles and Recent Applications

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