On the synthesis of β-bromohydrine ethers via intermolecular alkoxyl radical addition to bicyclo[2.2.1]heptene
作者:Jens Hartung、Nina Schneiders、Thomas Gottwald
DOI:10.1016/j.tetlet.2007.06.103
日期:2007.8
Primary, secondary, and tertiary alkoxyl radicals add exo-selectively to the olefinic π-bond in bicyclo[2.2.1]heptene to afford exo-2-alkoxybicyclo[2.2.1]hept-3-yl radicals, which are trapped with BrCCl3 preferentially from the endo face to furnish β-bromohydrine ethers in 23–67% yield.
Bond angles at thiohydroxamate oxygen in crystal structures of 3-alkoxy-5-(p-methoxyphenyl)-4-methylthiazole-2(3H)-thiones gradually increased with the size of the 3-alkoxy substituent. This effect was attributed to strain on the basis of (i) a linear free energy relationship (Taft-Dubois correlation) and (H) signal coalescence from resonances of diastereotopic CH3 groups in solution (O-cumyl substituent; DNMR). Substitution at oxygen along the sequence OR (R prim-, sec-, and tert-alkyl), CH, and OLi was reflected in a gradual decrease of N,O distances and lengthening of associated C,S bonds. The responsivity for these changes was more pronounced in the thiazole-2(3H)-thione than in the pyridine-2(1H)-thione series. (C) 2009 Elsevier Ltd. All rights reserved.
Spin trapping of alkoxyl radicals generated from 5-methyl and 5-aryl-3-alkoxy-4-methylthiazole-2(3H)-thiones in photochemically induced and microwave-initiated reactions
Methoxyl and isopropoxyl radicals were generated from N-alkoxy-4,5-dimethylthiazole-2(3H)-thiones (λmax∼320 nm) and 5-aryl derivatives (aryl=p-XC6H4; X=MeO, H, AcNH, Cl) (λmax∼335 nm) in photochemically and microwave-induced reactions. Alkoxylradicals were trapped with dimethylpyrrolidine N-oxide and characterized as spin adducts via EPR. Cumyloxyl radicals were liberated in a similar manner from
甲氧基和异丙氧基的基团从生成的ñ -烷氧基-4,5-二甲基噻唑-2(3 H ^)-thiones(λ最大~320纳米)和5-芳基衍生物(芳= p -XC 6 ħ 4 ; X =的MeO, H,AcNH,Cl)的(λ最大~335纳米)在光化学和微波诱导的反应。烷氧基被二甲基吡咯烷N-氧化物捕获并通过EPR表征为自旋加合物。枯基氧基以类似的方式从N-枯基氧基-5-(4-甲氧基苯基)-4-甲基噻唑-2(3 H)-硫酮中释放出来。N的最低能量跃迁发现了值得注意的红移- (羟基)茚并[2,1- d ]噻唑-2(3 H ^) -硫酮(λ最大= 376纳米),如果相比的UV-vis吸收ñ -羟基-4-甲基-5- phenylthiazole- 2(3 ħ) -硫酮(λ最大= 338纳米)。全面描述了烷氧基自由基前体的合成和进行N,O均解的程序。
Microwave-assisted generation of alkoxyl radicals and their use in additions, β-fragmentations, and remote functionalizations
solvents affords alkoxylradicals, which were identified by (i) spin adduct formation (EPR-spectroscopy) and (ii) fingerprint-type selectivities in intramolecular additions (stereoselective synthesis of disubstituted tetrahydrofurans), beta-fragmentations (formation of carbonyl compounds), and C,H-activation of aliphatic subunits, by delta-selective hydrogen atom transfer. C-Radicals formed from oxygen-centered