Enantioselective Halocyclization Using Reagents Tailored for Chiral Anion Phase-Transfer Catalysis

Wang, Yiming; Wu, Jeffrey C.S.; Hoong, Christina; Rauniyar, Vivek; Toste, F. Dean

doi:10.1021/ja305795x

Cited by 246 publications

(79 citation statements)

References 51 publications

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“…47 By employing insoluble, DABCO-derived, tricationic “Br + ” salts of the form 19 , in combination with a chiral, lipophilic phosphoric acid 20 (as a precursor to the chiral anion PT catalyst), highly enantioselective bromocyclizations of amido alkenes such as 18 could be achieved by solid-liquid phase transfer catalysis (Scheme 19). Similar results were obtained in iodocyclizations using an “I + ” salt analogous to 19 .…”

Section: Challenges For Stereoselective Catalysismentioning

confidence: 99%

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

2015

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Although recent years have witnessed significant advances in the development of catalytic, enantioselective halofunctionalizations of alkenes, the related dihalogenation of olefins to afford enantioenriched vicinal dihalide products remains comparatively underdeveloped. However, the growing number of complex natural products bearing halogen atoms at stereogenic centers has underscored this critical gap in the synthetic chemist's arsenal. This Review highlights the selectivity challenges inherent in the design of enantioselective dihalogenation processes, and formulates a mechanism-based classification of alkene dihalogenations, including those that may circumvent the "classical" haliranium (or alkene-dihalogen π-complex) intermediates. A variety of metal and main group halide reagents that have been used for the dichlorination or dibromination of alkenes are discussed, and the proposed mechanisms of these transformations are critically evaluated. AbstractCatalysis of alkene dihalogenation , under different activation modes, with control over both the absolute and relative stereochemical course of dihalogen addition, is one of the most vexing problems in stereoselective synthesis. Dihalogenations that circumvent the "classical" haliranium (or alkene-dihalogen π complex) intermediates provide new and exciting opportunities for catalysis, potentially having broader implications for the design of stereoselective alkene difunctionalizations.

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Section: Challenges For Stereoselective Catalysismentioning

confidence: 99%

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

2015

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“…However in these cases, instead of using conventional halogenating agents such as N-bromosuccinimide or N-iodosuccinimide, they had to develop new ionic brominating or iodinating agents 22, which are analogous to Selectfluor and are insoluble in organic solvents of low or moderate polarity (Scheme 8). 24 By using a chiral phosphate as the catalyst and with the help of these highly charged electrophilic halogenating agents, they were able to achieve 6-exo-cyclization to form the quaternary stereocenter-containing 4H-3,1-benzoxazines 24 with outstanding enantioselectivity. This operationally simple protocol works under mild reaction conditions and hence tolerates a variety of functionalities, including silyl ethers, unprotected alcohol, and tertiary amine groups.…”

Section: Scheme 2 the Catalytic Enantioselective Bromoaminocyclizatiomentioning

confidence: 99%

“…This operationally simple protocol works under mild reaction conditions and hence tolerates a variety of functionalities, including silyl ethers, unprotected alcohol, and tertiary amine groups. 24 Scheme 8 Enantioselective 6-exo-cyclization of benzamides to 4H-3,1-benzoxazines by Toste and co-workers 24 From the better mechanistic understanding that evolved with these developments, it was only logical that the various halocyclization reactions could also be applied to substrates other than simple olefins. Enantioselective halolactonizations of conjugated enynes 8 and alkynes 9 have already been reported.…”

Section: Scheme 2 the Catalytic Enantioselective Bromoaminocyclizatiomentioning

confidence: 99%

Catalytic Enantioselective Halocyclizations beyond Lactones: Emerging Routes to Enantioenriched Nitrogenous Heterocycles

Tripathi

Mukherjee

2013

Synlett

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Electrophilic halogen-induced reactions of unactivated olefins are an important class of transformations, whose catalytic enantioselective variants have surfaced during the past few years as effective means of olefin heterodifunctionalization. This article covers important developments in the area of enantioselective halocyclizations, specifically in the context of the synthesis of nitrogenous heterocycles.Stereoselective functionalization of unactivated olefins is possibly the most sought-after strategy for generating diversity from easily accessible starting materials. In this regard, the catalytic asymmetric homofunctionalization of unactivated olefins might be considered as a successful and rather mature area of research, thanks to the discovery of methods for epoxidation, dihydroxylation, aziridination, and, to some extent, diamination. Heterodifunctionalization, on the other hand, remained a relatively less well explored territory. Electrophilic halogen-induced activation of olefins followed by nucleophilic addition is a remarkably general strategy for stereoselective olefin heterodifunctionalization (Scheme 1). 1 Halolactonization [Scheme 1 (B); Nu = CO 2 H] is the most prominent example in this category. Even though halolactonization was discovered more than a century ago 2 and has been applied to the synthesis of numerous natural and nonnatural targets, 3 the development of catalytic enantioselective halolactonization and related halocyclization reactions has proved notoriously difficult. Because proven approaches to asymmetric catalysis failed when applied to halocyclization reactions, the field of asymmetric halocyclization was, until recently, virtually unexplored, except for some sporadic examples involving chiral phase-transfer catalysts and chiral Lewis acids. 4 The past few years have witnessed a renaissance in the area of enantioselective olefin halofunctionalization. 5,6 As expected, halolactonization was the first such reaction to catch the attention of researchers, and a number of methods for highly enantioselective chloro-, bromo-, and iodolactonization reactions were developed with the help of a range of structurally dissimilar catalysts. 7 These reactions were not restricted to olefins, as conjugated enynes 8 and alkynes 9 were also subjected to enantioselective halolactonizations. From these reports, the mechanistic pictures associated with these reactions became clearer and a foundation was laid for further developments. Subsequently, several other halocyclization reactions joined the Chandra Bhushan Tripathi (left) received his B.Sc.Scheme 1 Electrophilic halogen-induced stereoselective olefin functionalization (A) and its intramolecular variant, halocyclization (B) SYNLETT 2014, 25, 0163-0169 Advanced online publication: 03.12.20130 9 3 6 -5 2 1 4 1 4 3 7 -2 0 9 6

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“…This phenomenon always plays a significant role in Phase transfer catalysis (PTC), especially in organic synthesis. Phase-transfer catalysis (PTC) is well known as a precious methodology in organic synthesis in modern years [3,4] . Phase-transfer catalysis (PTC) is a performance that was conducting a reaction between reactant species existing in homogeneous or heterogeneous method [5] .…”

Section: Introductionmentioning

confidence: 99%

Kinetic study for benzyloxylation of p-bromotoluene using phase transfer catalyst assisted by microwave irradiation

Brahmayya

Wang

2016

Journal of the Taiwan Institute of Chemical Engineers

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Enantioselective Halocyclization Using Reagents Tailored for Chiral Anion Phase-Transfer Catalysis

Cited by 246 publications

References 51 publications

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

Catalytic Enantioselective Halocyclizations beyond Lactones: Emerging Routes to Enantioenriched Nitrogenous Heterocycles

Kinetic study for benzyloxylation of p-bromotoluene using phase transfer catalyst assisted by microwave irradiation

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