Dye-sensitized photooxygenation of 2,3-dihydrofurans: competing [2 + 2] cycloadditions and ene reactions of singlet oxygen with a rigid cyclic enol ether system
摘要:
Singlet oxygen reacts with 2,3-dihydrofuran (1), 5-methyl- (7), 4,5-dimethyl- (13), and 4-carbomethoxy-5-methyl-2,3-dihydrofuran (20), 5,6-dimethyl-3,4-dihydro-2H-pyran (26), and 3-methoxy-2-methyl-2-butene (32) in nonpolar and polar aprotic solvents to yield dioxetanes and allylic hydroperoxides, except 32, which gives only allylic hydroperoxides. The dioxetanes were isolated, but decompose slowly with weak chemiluminescence at room temperature to yield the corresponding dicarbonyl compounds. The allylic hydroperoxides produced by the cyclic enol ethers could not be isolated or separated by high vacuum distillation or by chromatography; the endocyclic allylic hydroperoxides arising from the dihydrofurans eliminate H2O2 to yield the corresponding furans while the exocyclic allylic hydroperoxides give unknown products. Allylic hydroperoxides 28 and 29 and the dioxetane 27 obtained from 26 yield the same dicarbonyl compound 31. The proportion of dioxetanes to allylic hydroperoxides depends on ring size and substitution of the enol ethers and on solvent polarity. Smaller ring size, greater electron-donor substitution, and solvent polarity favor the formation of dioxetanes at the expense of allylic hydroperoxides. It is noteworthy that enol ether 20, an alpha,beta-unsaturated ester, forms appreciable amounts of a dioxetane in polar solvents (44% in acetonitrile). Kinetic results show that the rate and product distribution of the ene reaction are independent of solvent polarity, whereas the rate of dioxetane formation increases with solvent polarity. It is suggested that [2 + 2] cycloadditions and ene reactions occur via different transition states and intermediates, zwitterions and perepoxides, respectively. Furthermore, the remarkable propensity to dioxetane formation of dihydrofurans compared to that of dihydropyrans and the other enol ethers seems to be due to the rigidity of the five-membered ring in the transition state and intermediate zwitterion.
Alcohol Synthesis by Cobalt-Catalyzed Visible-Light-Driven Reductive Hydroformylation
作者:Connor S. MacNeil、Lauren N. Mendelsohn、Tyler P. Pabst、Gabriele Hierlmeier、Paul J. Chirik
DOI:10.1021/jacs.2c07745
日期:2022.10.26
A cobalt-catalyzed reductive hydroformylation of terminal and 1,1-disubstituted alkenes is described. One-carbon homologated alcohols were synthesized directly from CO and H2, affording anti-Markovnikov products (34–87% yield) with exclusive regiocontrol (linear/branch >99:1) for minimally functionalized alkenes. Irradiation of the air-stable cobalt hydride, (dcype)Co(CO)2H (dcype = dicyclohexylphosphinoethane)
描述了钴催化的末端和 1,1-二取代烯烃的还原加氢甲酰化。一碳同系醇直接从 CO 和 H 2合成,提供抗马尔可夫尼科夫产品(34-87% 产率),对最小功能化烯烃具有独特的区域控制(线性/支链 >99:1)。用蓝光照射空气稳定的氢化钴 (dcype)Co(CO) 2 H(dcype = 二环己基膦基乙烷)产生了介导烯烃加氢甲酰化和随后的醛氢化的活性催化剂。通过使用合成气混合物的多核 NMR 光谱对串联催化反应进行原位监测,研究了绝对区域控制的机理起源。
Bicyclic vinyl sulfides by ring expansions of spirocyclic dithioketal systems
作者:Alex Nickon、Abimael D. Rodriguez、Vilas Shirhatti、Rathindra Ganguly
DOI:10.1021/jo00222a008
日期:1985.11
Indoles
作者:I. I. Grandberg、S. N. Dashkevich
DOI:10.1007/bf00476820
日期:1971.6
1,2-Dioxetanes derived from 4,5-dimethyl-2,3-dihydrofuran and 4,5-dimethyl-2,3-dihydrothiophene. Synthesis via photooxygenation, activation parameters, and excitation properties
作者:Waldemar Adam、Axel G. Griesbeck、Klaus Gollnick、Karen Knutzen-Mies
DOI:10.1021/jo00242a028
日期:1988.4
Decor,J.-P.; Descotes,G., Bulletin de la Societe Chimique de France, 1970, p. 2370 - 2376