Tertiary alkoxyl radicals from 3-alkoxythiazole-2(3H)-thiones

Schur, Christine; Becker, Nina; Bergsträßer, Uwe; Gottwald, Thomas; Hartung, Jens

doi:10.1016/j.tet.2010.12.071

Cited by 16 publications

(11 citation statements)

References 59 publications

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“…The intermediate formed by adding, for example, the trichloromethyl radical to the thione sulfur of MTTOR 1 dissociates into 2-(trichloromethylsulfanyl)-4-methylthiazole 2 and oxygen radical I (Scheme 1). 14 4-Pentenoxyl radicals cyclize by intramolecularly adding with rate constants of 10 8 -10 9 s −1 at room temperature to a terminal double bond, providing tetrahydrofuranylmethyl radicals, for example II, in a fingerprint 5-exo/6-endo-regioselectivity of 98 : 2. 17 Trapping of carbon radical II by bromotrichloromethane yields bromomethyltetrahydrofuran 3 as a target product, and the trichloromethyl radical for propagating the chain reaction.…”

Section: Results and Interpretationmentioning

confidence: 99%

“…To understand the origin of 2,4cis-selectivity, we modelled transition structures (TS) of 2-allylcyclohexyl-1-oxyl radical 5-exo-cyclization Ic → IIc, using assessed electronic structure methods. 14,52 For stereochemical analysis, we considered transition structures for 2,4-cis-(TS 1 ) and 2,4-trans-cyclization (TS 2 ) of allylcyclohexyloxyl radicals cis/trans-Ic ( Fig. 4 and ESI; ‡ see also section 2.4).…”

Section: Results and Interpretationmentioning

confidence: 99%

“…For calculating equilibrium structures of conformational flexible molecules and transition structures associated with radical addition to carbon-carbon double bonds we used an established strategy. 8,14 According to theory, the 2-(cyclohexen-3-yl)-ethyloxyl radical Ii favors a Protons experiencing deshielding by changing the position of the carbon-bromine bond from anti to syn, and vice versa, are printed in blue. pseudo-equatorial ( pe) positioning of the ethyloxyl radical side to pseudo-axial ( pa), as expressed by a modelled 90/10-mixture of pe/pa-conformers of Ii at 298 K (B3LYP/6-31+G**; ESI ‡).…”

Section: Strain Effects In Alkoxyl Radical Additionsmentioning

confidence: 99%

“…[7][8][9] Stereodifferentiation by alkyl or aryl groups arises from steric effects, which gradually increases as the distance between a controlling substituent and the attacked π-bond shortens, for example from a 15/85-cis/trans-ratio at room temperature to <2/98 by shifting a tert-butyl group from position 1 to position 3. 8 In synthesis, 5-exocyclized 4-pentenoxyl radicals are preferentially trapped by a heteroatom atom donor, 10,11 for introducing halogen, [12][13][14] alkylsulfanyl, 15 or other synthetically useful functional groups. 16 The model to explain stereodifferentiation by a carbon substituent in 4-pentenoxyl radical cyclization predicts that the intramolecular addition proceeds via a distorted twistconformer of tetrahydrofuran as the favored transition structure (twist-model), 8,17 differing from the cyclohexane-based Beckwith-Houk-model for carbon radical cyclization.…”

Section: Introductionmentioning

confidence: 99%

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Annulated and bridged tetrahydrofurans from alkenoxyl radical cyclization

et al. 2014

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4-Pentenoxyl radicals sharing two or more carbon atoms with a cycloalkane cyclize in a predictable manner stereoselectively and regioselectively to afford in solutions of bromotrichloromethane cycloalkyl-fused or -bridged 2-bromomethyltetrahydrofurans in up to 95% yield. Stereoselectivity in alkenoxyl radical ring closures arises from cumulative steric effects. The substituent positioned the closest to the alkene carbon, which is being attacked by the oxygen radical, exerts the strongest stereodirecting effect. This principal inductor guides 5-exo-cyclization 2,3-trans- or 2,4-cis-selectively. The substituent located further from the attacked π-bond is the secondary inductor. A secondary inductor in the relative trans-configuration enhances stereodifferentiation by the primary inductor; a cis-configured secondary inductor decreases this effect. A secondary inductor is not able to overrule the guiding effect of a similar sized primary inductor. Intramolecular 4-pentenoxyl radical additions to a cyclohexene-bound exo-methylene group or to endocyclic double bonds proceed cis-specifically, as exemplified by synthesis of a diastereomerically pure bromobicyclo[2.2.1]heptyl-annulated tetrahydrofuran from the verbenylethyloxyl radical. According to theory, the experimental 2,3-cis-specificity in alkoxyl radical cyclization to an endocyclic π-bond arises from strain associated with the 2,3-trans-ring closure.

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Section: Results and Interpretationmentioning

confidence: 99%

Section: Results and Interpretationmentioning

confidence: 99%

Section: Strain Effects In Alkoxyl Radical Additionsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Annulated and bridged tetrahydrofurans from alkenoxyl radical cyclization

et al. 2014

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“…[3] Furthermore, (cyclic) organic dithiocarbamates are used as substrates for radical chemistry [4][5][6] and as synthetic intermediates toward thiourea, amidines, and guanidines. [7][8][9] The latest report for synthesis of unfused 3,6-dihydro-2H-1,3-thiazine-2-thiones dates back to 2012, when Romano et al reported the treatment of 1-azadienes with carbon disulfide.…”

Section: Introductionmentioning

confidence: 99%