p-MeOC6H4/TiCl3: a novel initiator for halogen atom-transfer radical reactions in aqueous media

Cao, Lidong; Li, Chaozhong

doi:10.1016/j.tetlet.2008.10.070

Cited by 35 publications

(10 citation statements)

References 48 publications

(6 reference statements)

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“…13 C NMR(101 MHz, CDCl3) δ = 171.4, 145.6, 135.0, 129.9, 128.3, 53.0, 39.7, 33.9, 21.8, 7.3. All analytical data were in good accordance with reported data 21. 4-(Iodomethyl)-4-methyl-1-tosylpyrrolidin-2-one (2b) Yield: 266 mg (68%); white solid; mp 156.3-158.6 °C.1…”

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confidence: 84%

Tetrahydroxydiboron-Initiated Atom-Transfer Radical Cyclization

Wang¹,

Li²,

Wang³

2021

Synthesis

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In this work, the first diboron reagent initiated atom-transfer radical cyclization was reported, in which the boryl radicals were generated by the homolytic cleavage of a B-B single bond weakened by the coordination of Lewis base. To clarify the role of carbonate and DMF in the cleavage of B-B bond, we calculated the free energy diagram of two pathways by density functional theory (DFT) investigations. The DFT calculation showed that the presence of carbonate facilitates the B-B bond cleavage to form boron radicals which can be further stabilized by DMF. Subsequent atom transfer cyclization initiated by stabilized dihydroxyboron radical are also energetically favored.

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confidence: 84%

Tetrahydroxydiboron-Initiated Atom-Transfer Radical Cyclization

Wang¹,

Li²,

Wang³

2021

Synthesis

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“…As an example, the 5- exo cyclization of N -ethoxycarbonyl-substituted iodoamides 24a − 24c under the above optimized conditions with Mg(ClO 4 ) 2 / L2 led to the exclusive formation of 25a − 25c as single stereoisomers in almost quantitative yields (eq ). Compared to literature reports, a much better control of stereoselectivity was achieved under milder conditions. …”

Section: Resultsmentioning

confidence: 99%

Efficient Regio- and Stereoselective Formation of Azocan-2-ones via 8-Endo Cyclization of α-Carbamoyl Radicals

Fang

Liu

2010

J. Am. Chem. Soc.

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The iodine-atom-transfer 8-endo cyclization of alpha-carbamoyl radicals was investigated experimentally and theoretically. With the aid of Mg(ClO(4))(2) and a bis(oxazoline) ligand, N-ethoxycarbonyl-substituted N-(pent-4-enyl)-2-iodoalkanamides underwent 8-endo cyclization leading to the formation of only the corresponding 3,5-trans-substituted azocan-2-ones in excellent yields. Similarly, the BF(3).OEt(2)/H(2)O-promoted reactions of N-ethoxycarbonyl-N-(2-allylaryl)-2-iodoalkanamides afforded exclusively the benzazocanone products with a 3,5-cis configuration in high yields. The bidentate chelation of substrate radicals not only significantly improved the efficiency of cyclization but also resulted in the change of stereochemistry of azocanone products from 3,8-trans to 3,8-cis. Theoretical calculations at the UB3LYP/6-31G* level revealed that the cyclization of N-carbonyl-substituted alpha-carbamoyl radicals occurs via the E-conformational transition states without the presence of a Lewis acid. On the other hand, the cyclization proceeds via the Z-conformational transition states when the substrates form the bidentate chelation with a Lewis acid. In both cases, the 8-endo cyclization is always fundamentally preferred over the corresponding 7-exo cyclization. The complexed radicals having the more rigid conformations also allow the better stereochemical control in the iodine-atom-abstraction step. To further understand the reactivity of alpha-carbamoyl radicals, the competition between the 8-endo and 5-exo cyclization was also studied. The results demonstrated that the 8-endo cyclization is of comparable rate to the corresponding 5-exo cyclization for alpha-carbamoyl radicals with fixed Z-conformational transition states. As a comparison, the 8-endo mode is fundamentally preferred over the 5-exo mode in the cyclization of NH-amide substrates because the latter requires the Z-conformational transition states, whereas the former proceeds via the more stable E-conformational transition states.

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“…The corresponding ATRA with derivatives of iodoacetic acid has been less studied (Scheme , B ). Esters of iodoacetic acid have been employed utilizing stoichiometric amounts of initiators, triethylborane, Ti, or Cu, leading to either the ATRA product or the cyclized lactone. Using iodoacetic acid and stoichiometric AIBN, Oshima synthesized lactones, while Zhu employed bromodifluoroamides of acetic acid to access lactams …”

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confidence: 99%