4136-86-1Relevant articles and documents
Generation of Functionalized Alkyl Radicals via the Direct Photoexcitation of 2,2′-(Pyridine-2,6-diyl)diphenol-Based Borates
Miyamoto, Yusuke,Sumida, Yuto,Ohmiya, Hirohisa
supporting information, p. 5865 - 5870 (2021/07/31)
A new type of alkylborate was developed for the purpose of generating radicals via direct photoexcitation. These borates were prepared using 2,2′-(pyridine-2,6-diyl)diphenol as a tridentate ligand together with organoboronic acids or potassium trifluoroborates. The ready availability of organoboron compounds is a significant advantage of this direct photoexcitation protocol. The excited states of these borates can also serve as strong reductants, enabling various transformations.
Synergetic Catalysis for One-pot Bis-alkoxycarbonylation of Terminal Alkynes over Pd/Xantphos?Al(OTf)3 Bi-functional Catalytic System
Guo, Wen-Di,Liu, Lei,Yang, Shu-Qing,Chen, Xiao-Chao,Lu, Yong,VO-Thanh, Giang,Liu, Ye
, p. 1376 - 1384 (2020/01/24)
Tandem bis-alkoxycarbonylation of alkynes allows for the preparation of 2-substituted succinates from alkynes and nucleophile alcohol via two successive alkoxycarbonylation with advantages of 100 % atomic economy and simplified one-pot operation. Herein, the one-pot tandem bis-alkoxycarbonylation of alkynes was accomplished over the bi-functional catalytic system containing Xantphos-modified Pd-complex and Lewis super-acid of Al(OTf)3. It was found that, via the synergetic catalysis, the involved Xantphos-modified Pd-complex was responsible for the activation of CO and the alkynes through coordination to Pd-center while Al(OTf)3 was in charge of the activation of the alcohol to facilitate the formation of [Pd?H]+ active species. The in situ high-pressure FT-IR analysis, coupled with 1H/13C NMR spectral characterizations, confirmed that the introduced Al(OTf)3 with intensive oxophilicity (via acid-base pair interaction) was able to activate nucleophilic MeOH to be a reliable proton-donor (i. e. hydride-source) to warrant the formation and stability of [Pd?H]+ species upon the oxidation of Pd0 by H+ (Pd0+H+→[PdII?H]+). Over the developed bi-functional catalytic system, the yields of the target diesters were obtained in the range of 36~86 % in this sequence with the wide substrate scope.
Electron-Transfer-Photosensitized Conjugate Alkylation
Fagnoni, Maurizio,Mella, Mariella,Albini, Angelo
, p. 4026 - 4033 (2007/10/03)
Photoinduced electron transfer (PET) from an aliphatic donor to a sensitizer and fragmentation of the radical cation leads to alkyl radicals. Radical alkylation of electron-withdrawing substituted alkenes and alkynes has been obtained in this way, and its scope has been explored. Effective sensitizers are tetramethyl pyromellitate (TMPM), 1,4-dicyanonaphthalene (in combination with biphenyl, DCN/BP), and 1,2,4,5-tetracyanobenzene. Radical precursors are tetraalkylstannanes, 2,2-dialkyldioxolanes, and, less efficiently, carboxylic acids. Steady-state and flash photolysis experiments show that escape out of cage of radical ions is the main factor determining the yield of radical formation. This is efficient with triplet sensitizers such as TMPM, while with singlet sensitizers, the use of a "cosensitizer" is required, as in the DCN/BP system. Radical cations containing primary alkyl radicals escape and fragment more efficiently than those containing tertiary radicals. The thus-formed radicals are trapped by electron-withdrawing substituted alkenes, and the relative efficiency is determined by the rate of radical addition, in accord with the proposed mechanism. Among the alkynes tested, only dimethyl acetylenedicarboxylate reacts, and the order of radical reactivity is different. It is suggested that a different mechanism operates in this case and involves assistance by the alkyne to the radical cation fragmentation.