Synthesis of cyclobutane lignans via an organic single electron oxidant–electron relay system

Riener, Michelle; Nicewicz, David A.

doi:10.1039/c3sc50643f

Cited by 163 publications

(125 citation statements)

References 41 publications

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“…Then atural product magnosalin (2f)w as prepared by dimerization in 43 %yield. [10] It was also possible to dimerize av ariety of alkenes whereby the methyl group had been replaced by either al onger chain (2g)o ramore functionalized chain (2i-k). Steric hinderance retarded cyclization, as evidenced by the slow (and lower yielding) formation of the cyclobutane 2h bearing two isopropyl groups.…”

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confidence: 99%

Catalytic Hypervalent Iodine Promoters Lead to Styrene Dimerization and the Formation of Tri‐ and Tetrasubstituted Cyclobutanes

2016

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Reported herein is that the use of catalytic quantities of hypervalent iodine reagents (phenyliodine diacetate or Dess-Martin periodinane) allows the rapid and stereoselective formation of cyclobutanes under very mild reaction conditions. The presence of a fluorinated solvent is essential for the success of these reactions which form unsymmetrical tri- and tetrasubstituted cyclobutanes through a heterodimerization process involving two different alkenes.

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Catalytic Hypervalent Iodine Promoters Lead to Styrene Dimerization and the Formation of Tri‐ and Tetrasubstituted Cyclobutanes

2016

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“…Interestingly, 1,2-dialkoxybenzenes are recalcitrant to the reaction conditions, possibly due to insufficient charge density at the other four sites on the ring. 36 However, we discovered that changing one of the alkoxy groups to a more electron-deficient tosylate, as in 2s , rendered this 1,2-dialkoxybenzene reactive, giving a single regioisomer of the benzonitrile 3s .…”

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Direct C–H Cyanation of Arenes via Organic Photoredox Catalysis

2017

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Methods for the direct C-H functionalization of aromatic compounds are in demand for a variety of applications, including the synthesis of agrochemicals, pharmaceuticals, and materials. Herein, we disclose the construction of aromatic nitriles via direct C-H functionalization using an acridinium photoredox catalyst and trimethylsilyl cyanide under an aerobic atmosphere. The reaction proceeds at room temperature under mild conditions and has proven to be compatible with a variety of electron-donating and -withdrawing groups, halogens, and nitrogen-and oxygencontaining heterocycles, as well as aromatic-containing pharmaceutical agents.Nitrile-containing aromatic groups are well represented throughout agrochemicals and therapeutic molecules (Scheme 1A). In addition to being prevalent in a number of bioactive compounds, cyanoarenes provide an excellent functional group handle that can be transformed to give derivatives of benzoic acid through hydrolysis, 1 aryl ketones or imines after treatment with a strong nucleophile, 2 benzaldehydes or benzylamines by reduction, 3 aryl-amides through hydration, and even tetrazoles through [3+2] cycloadditions with sodium azide. 4 Classical approaches to cyanoarene synthesis include the Sandmeyer reaction from the corresponding diazonium salt 5 or transition-metal-catalyzed cross-coupling with the requisite aryl halide. 6-14 Few C-H functionalization methods exist for directly producing benzonitriles from unfunctionalized arenes, and they employ Rh or Co catalyst systems, often requiring elaborate directing groups and exotic reagents, 15-20 harsh lithiation conditions, 21 or electrophilic sources of cyanide that give poor selectivity or significant byproduct formation. 22 While the aforementioned methods are successful at accessing arene cyanation, a mild and metal-free C-H cyanation of aromatic compounds employing a common and inexpensive cyanide source has yet to be reported. Experimental procedures and supporting data 1 H and 13 C NMR spectra (PDF)The authors declare no competing financial interest. HHS Public Access Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptRecent efforts from our laboratory have demonstrated the reactivity of arene cation radicals, 23 generated via photoinduced electron transfer from the excited state of an acridinium catalyst, 24 to accomplish direct C-H amination of a range of aromatics and heteroaromatics bearing a variety of functional groups. 25 Importantly, this transformation does not require the presence of a directing group and is highly para-selective for monosubstituted benzenes. [26][27][28] Recognizing the importance of cyanoaromatics, and previous literature citing the addition of cyanide to arene radical cations, 29,30 we decided to investigate the use of cyanide nucleophiles in reactions with arene cation radicals to access this class of compounds. We proposed that the highly oxidizing 3,6-di-tert-butyl-9-mesityl-10-phenylacridinium tetrafluoroborate (1, E 1/2 red * = +2.15 V vs SCE) 25 would be an effecti...

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“…The photochemical [2+2] reaction has factored significantly in the total synthesis of symmetrical truxillic acid and related derivatives, [7] including elegant solutions from crystal engineering [8] and advances from redox photocatalysis. [9] Alternatively, truxinic acid derivatives have been formed in modest diastereoselectivity by [2+2] photocycloaddition in flow. [10] However, direct photodimerization is extremely limited for the construction of cyclobutane natural products where the core is chiral and the alkene precursors are non-equivalent such as the compounds displayed in Figure 1.…”

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A Mixed‐Ligand Chiral Rhodium(II) Catalyst Enables the Enantioselective Total Synthesis of Piperarborenine B

2016

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A novel, mixed-ligand chiral rhodium(II) catalyst, Rh2(S-NTTL)3(dCPA), has enabled the first enantioselective total synthesis of the natural product piperarborenine B. A crystal structure of Rh2(S-NTTL)3(dCPA) reveals a “chiral crown” conformation with a bulky dicyclohexylphenyl acetate ligand and three N-naphthalimido groups oriented on the same face of the catalyst. The natural product was prepared on large scale using rhodium-catalyzed bicyclobutanation/copper-catalyzed homoconjugate addition chemistry in the key step. The route proceeds in ten steps with an 8% overall yield and 92% ee.

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Synthesis of cyclobutane lignans via an organic single electron oxidant–electron relay system

Cited by 163 publications

References 41 publications

Catalytic Hypervalent Iodine Promoters Lead to Styrene Dimerization and the Formation of Tri‐ and Tetrasubstituted Cyclobutanes

Catalytic Hypervalent Iodine Promoters Lead to Styrene Dimerization and the Formation of Tri‐ and Tetrasubstituted Cyclobutanes

Direct C–H Cyanation of Arenes via Organic Photoredox Catalysis

A Mixed‐Ligand Chiral Rhodium(II) Catalyst Enables the Enantioselective Total Synthesis of Piperarborenine B

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