Stepwise Electrophilic Addition. Some Novel Synthetic Ramifications of an Old Concept

Smit, W. A.; Caple, R.; Smoliakova, Irina P.

doi:10.1021/cr00032a006

Cited by 67 publications

(33 citation statements)

References 7 publications

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“…Thus, the solvent has a significant influence on the potential energy surface. To conclude, a concerted addition mechanism is found for the observed reaction, which is different from the traditional stepwise addition mechanism 9…”

Section: Resultscontrasting

confidence: 59%

A Novel Addition Mechanism for the Reaction of “Frustrated Lewis Pairs” with Olefins

Guo

2008

Eur J Inorg Chem

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Density functional theory calculations have been carried out to investigate the addition mechanism for the reactions of "frustrated Lewis pairs" with olefins. Several reactions are studied in this work, which include a three-component reaction between a sterically demanding phosphane [P(tBu) 3 ], borane [B(C 6 F 5 ) 3 ], and ethylene, and a two-component reaction between an olefin derivative of phosphane [CH 2 =CH-(CH 2 ) 3 P(tBu) 2 ] and B(C 6 F 5 ) 3 . For the two-component reaction, we find a concerted addition mechanism, in which the formation of the B-C and P-C bonds takes place simultaneously. For the three-component reaction, our calculations show that the reaction may be initiated by the weak association of B(C 6 F 5 ) 3 with ethylene (to form a transient species) and then proceeds in a concerted transition state similar to

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Section: Resultscontrasting

confidence: 59%

A Novel Addition Mechanism for the Reaction of “Frustrated Lewis Pairs” with Olefins

Guo

2008

Eur J Inorg Chem

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“…One viable approach to improve the stereoselectivity in organic synthesis has been the use of epoxides [165,166] or three-membered cyclic cations (e.g., episulfoniium [167][168][169][170][171] and episelenonium [172,173]). Reactions of nucleophiles with these species are expected to proceed with high stereoselectivity as a In the absence of AgClO 4, the reaction did not proceed result of trans-opening of the rings [165,166] or three-membered cyclic cations (e.g., episulfonium [167][168][169][170][171] and episelenonium [172,173]). Epoxides and threemembered cyclic ions have been the precursors for the preparation of O-glycosides [174][175][176][177].…”

Section: Superarmed Glycosyl Donors In Glycosylation Reactionsmentioning

confidence: 99%

“…Episulfonium ions have been known to react with a variety of nucleophiles of different natures and strengths [2,167,[169][170][171]. …”

Section: Superarmed Glycosyl Donors In Glycosylation Reactionsmentioning

confidence: 99%

Armed-Disarmed Concept in the Synthesis of Glycosidic Bond

Miljković

2013

Electrostatic and Stereoelectronic Effects in Carbohydrate Chemistry

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-Reid et al. reported [1] that n-pentenyl glycosides undergo chemospecific cleavage 1 ! 2 ! 3, with N-bromosuccinimide under conditions that leave a wide variety of other protecting groups unaffected ( Fig. 5.1).According to the proposed mechanism ( Fig. 5.1), the addition of water to the reaction mixture will lead to hydrolysis but the addition of alcohol or another sugar having a free hydroxyl group will lead to the formation of glycoside or a disaccharide. In the course of these studies, Fraser-Reid et al. [1] observed that sugar molecules having an acyloxy group at the C2 carbon (6 in Fig. 5.2) hydrolyzed much more slowly than if they had an alkoxy group (7 in Fig. 5.2). This observation suggested that the n-pentenyl glycoside could be made more or less reactive (it could be armed or disarmed) by the type of protecting group placed on the C2 oxygen.The ability of the C2 acyloxy group to disarm the n-pentenyl glycoside was rationalized as shown in Fig. 5.3. Thus, it can be assumed that the cyclic halonium ions 8 and 9 are formed reversibly [2] and that the electron density on the glycosidic oxygen is depleted in 2-O-acyl derivatives so that nucleophilic attack of this oxygen on the halonium ion is less favored than in the 2-O-alkyl counterpart 9. The reason for this is that the electron-withdrawing group at the C2 carbon makes the C2 carbon slightly positively charged so that the formation of another positive charge at the C1 carbon is not a favorable process [there cannot exist two positive charges on two neighboring carbons (C1 and C2) (Fig. 5.3).].Consequently, the armed glycosyl donors react with electrophiles faster than the disarmed ones, and therefore in a solution containing both an armed and disarmed glycosyl donor molecules, whereby disarmed glycosyl donor molecules have one free hydroxyl group, the reaction with an electrophile will result in crosscoupling and not self-coupling, i.e., an armed glycosyl donor will react with the disarmed one, whereas a disarmed donor will not react with itself [3] as illustrated in Fig. 5.5. The promoters for the activation of n-pentenyl group [4,5] are iodonium dicollidine perchlorate (IDCP) and N-iodosuccinimide/triethylsilyl triflate (NIS/Et 3 SiOTf).M. Miljkovic, Electrostatic and Stereoelectronic Effects in Carbohydrate Chemistry,

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“…Smit and Caple have investigated this process extensively, and found that a number of carbocations, and arenesulfenium and nitronium ions are able to initiate this process [26]. Among carbocations, the majority of attention has been paid to a wide variety of acylium ions, but 3 o alkyl carbenium ions (t-butyl, adamantyl), α-arylthio carbenium ions, and even another propargylcobalt cation have been employed to initiate this process.…”

Section: Reactions Of Enyne Complexesmentioning

confidence: 99%

Chemistry of Propargyldicobalt Cations Recent Developments in the Nicholas and Related Reactions

Green

2001

COC

145

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Abstract:The chemistry of propargyldicobalt cations, also known as the Nicholas reaction, is reviewed, with a focus on the developments since 1995. Advances in the understanding of the fundamental properties, such as structure, stability, and reactivity, of both the hexacarbonyl complexes and those bearing other ligands are discussed. All reactions involving propargyl cation dicobalt complexes are covered, including those stemming from ionization of propargylic leaving groups and those created by electrophilic addition to enyne complexes. Migration reactions involving either initiation or termination by propargyl cation complexes are included, as are the generation and reactions of propargyldicobalt radicals. Cyclization reactions employing these cations have received much attention, in cases with the alkynedicobalt unit located in both exocyclic and endocyclic positions, and these reports are described. Particular attention is paid to preparation of medium ring cycloalkyne complexes and their heterocyclic analogues. In addition, there is discussion of the progress in the in selectivity of these reactions, especially in terms of introduction of asymmetry at the propargylic site. Finally, recent applications of Nicholas reaction chemistry in the synthesis of natural products and related compounds are reported.

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Stepwise Electrophilic Addition. Some Novel Synthetic Ramifications of an Old Concept

Cited by 67 publications

References 7 publications

A Novel Addition Mechanism for the Reaction of “Frustrated Lewis Pairs” with Olefins

A Novel Addition Mechanism for the Reaction of “Frustrated Lewis Pairs” with Olefins

Armed-Disarmed Concept in the Synthesis of Glycosidic Bond

Chemistry of Propargyldicobalt Cations Recent Developments in the Nicholas and Related Reactions

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