Enantiospecific Synthesis of Vicinal Stereogenic Tertiary and Quaternary Centers by Combination of Configurationally-Trapped Radical Pairs in Crystalline Solids

Ellison, Martha; Ng, Danny; Dang, Hung; Garcı́a-Garibay, Miguel A.

doi:10.1021/ol0347803

Cited by 29 publications

(18 citation statements)

References 15 publications

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“…Notably, both samples reacted efficiently and in a completely diastereospecific manner when reactions were carried out to 60% conversion. Sample of ( þ )-(2R,4S)-187 gave the corresponding combination product in 100% ee and de, suggesting a small amount of inversion at one carbon center, but not at both[79].…”

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confidence: 99%

CarbonCarbon Bond Formation by the Photoelimination of Small Molecules in Solution and in Crystals

Shiraki

2009

Handbook of Synthetic Photochemistry

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The formation of CÀC bonds is arguably the most important reaction in organic synthesis. While many strategies have been developed to link organic fragments with a wide range of thermal processes, photochemical syntheses based on the elimination of a small molecule, X (Scheme 2.1), offer significant advantages when the desired structures are highly strained or hindered. In this chapter, we will describe examples of the generation of CÀC bonds through the photoinduced extrusion of small molecules such as N 2 , CO 2 , CO, and SO 2 , as well as the formal extrusion of S atoms. After describing the most general mechanistic aspects covering these reactions and the current scope and limitations, we will illustrate examples involving these reactions in solution. Following that, we will describe a strategy based on the use of crystalline solids that helps to control the fate of the reaction intermediates. Finally, we will illustrate the use of crystalline ketones (X¼CO) as one of the most promising general methods for the synthesis of compounds with all-carbon adjacent stereogenic quaternary centers.The photoelimination of a small stable molecule X accompanied by the formation of a new CÀC bond could, in principle, take place in a concerted manner through cyclic transition states with simultaneous bond-breaking and bond-making steps that follow trajectories determined by orbital symmetry considerations. However, as it pertains to photodecarbonylation reactions, theoretical analysis on the formation of hydrogen and CO from formaldehyde suggests that the concerted process is significantly less likely than the stepwise cleavage of the HÀC(O)ÀH bonds [1]. Similar conclusions have been made for the elimination of N 2 and H 2 from simple diazene (HN¼NH) [2]. In fact, evidence for concerted reactions is available only in a handful of cases (vide infra). Most examples involve a four-step process that starts with electronic excitation (step 1) and is followed by an a-cleavage reaction (step 2) to give a primary biradical or radical pair (BR-1). Subsequent dissociation of the small molecule X (step 3) results in the formation of the secondary biradical or radical pair (BR-2), which is followed by radical-radical combination to give the desired product (step 4).Handbook of Synthetic Photochemistry. Edited

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confidence: 99%

CarbonCarbon Bond Formation by the Photoelimination of Small Molecules in Solution and in Crystals

Shiraki

2009

Handbook of Synthetic Photochemistry

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“…8 While the reaction is ideal for the synthesis of molecules with adjacent quaternary stereogenic centers,9 its application for the synthesis of enantiomerically pure natural products has not been demonstrated 10. 11 With that in mind, we report here a very efficient synthesis of the natural product (α)‐cuparenone ( 1 ), in which the two quaternary centers are formed in the crystalline state with complete stereocontrol (Scheme ).…”

Section: Methodsmentioning

confidence: 99%

Parallel Syntheses of (+)‐ and (−)‐α‐Cuparenone by Radical Combination in Crystalline Solids

Natarajan

Yang

et al. 2007

Angew Chem Int Ed

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“…Reactions with chiral crystals occurred with quantitative enantiomeric yields and >95% diastereomeric yields (Scheme 78). 111 The spatial orientation of the substituents at C2 and C4 in the starting ketone is maintained at stereocenters C2 and C3 in the product.…”

Section: Aldol and Mannich Reactionsmentioning

confidence: 99%

Enantioselective synthesis of all-carbon quaternary stereogenic centers in acyclic systems

2011

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Most of the methods for the creation of all-carbon quaternary stereogenic centers in acyclic systems were developed in the last decade showing the contemporary interest of this field of research. Initial strategies, where chiral entities were linked to carbon skeleton, to enantioselective catalysis and finally to strategies where several carbon-carbon bonds were created in a single-pot operation, reflect the constant strive and creativity in the design and execution of synthetic sequences. This feature article summarizes these sequences and is divided into sections on substitution and additions reactions, alkylation, aldol, Mannich and rearrangements reactions. It is safe to predict that this field of chemistry will continue to grow exponentially in the coming decades and the ready availability of a wide range of these chiral entities will provide an excellent opportunity to further enrich mainstream synthetic methodologies.

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Enantiospecific Synthesis of Vicinal Stereogenic Tertiary and Quaternary Centers by Combination of Configurationally-Trapped Radical Pairs in Crystalline Solids

Cited by 29 publications

References 15 publications

CarbonCarbon Bond Formation by the Photoelimination of Small Molecules in Solution and in Crystals

CarbonCarbon Bond Formation by the Photoelimination of Small Molecules in Solution and in Crystals

Parallel Syntheses of (+)‐ and (−)‐α‐Cuparenone by Radical Combination in Crystalline Solids

Enantioselective synthesis of all-carbon quaternary stereogenic centers in acyclic systems

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