3395-81-1Relevant articles and documents
Systematic Study of Regioselective Reductive Ring-Opening Reactions of 4,6- O-Halobenzylidene Acetals of Glucopyranosides
Mez?, Erika,Herczeg, Mihály,Demeter, Fruzsina,Bereczki, Ilona,Csávás, Magdolna,Borbás, Anikó
, p. 12973 - 12987 (2021/09/18)
Reductive openings of cyclic acetals are widely used in modern synthetic organic chemistry for the regioselective introduction of protecting groups. A systematic study was performed on the applicability and efficacy of various hydride donor and protic or Lewis acid reagent combinations in the reductive ring opening of glucosidic 4,6-halobenzylidene acetals bearing an ortho-, meta-, and para-chloro- or -bromo substituent on the benzene ring. Most of the reagent combinations tested cleaved the 4,6-O-halobenzylidene acetal rings at O4 or O6 efficiently and with the expected regioselectivity. The LiAlH4-AlCl3 and the BH3·THF-TMSOTf combinations produced the 4-O-halobenzyl ether/6-OH products with complete regioselectivity and high yields. The use of Me3N·BH3-AlCl3 reagent system in toluene was also effective in cleaving the acetal ring at O6 but was accompanied by Al-chelation-assisted debenzylation side reactions. The NaCNBH3-HCl and the Et3SiH-BF3·Et2O combinations were highly effective in yielding the 6-halobenzyl ether/4-OH derivatives. Et3SiH, in combination with TfOH, produced the 6-O-ether/4-OH products in rapid reactions but also triggered silylation and reductive halobenzylation as secondary transformations. Reductive opening of the 1,3-dioxane ring of pyranosidic 4,6-O-halobenzylidene acetals by the proper reagent combination was found to be an efficient method for the regioselective introduction of versatile halobenzyl protecting groups onto the pyranose ring.
Thiol-initiated photocatalytic oxidative cleavage of the C=C bond in olefins and its extension to direct production of acetals from olefins
Wang, Xinglin,Li, Yuanyuan,Li, Zhaohui
, p. 1000 - 1006 (2021/02/26)
The oxidative cleavage of olefins to produce aldehydes/ketones is an important reaction in organic syntheses. In this manuscript, a mild and operationally simple protocol for the aerobic oxidation of olefins to produce carbonyl compounds was realized over ZnIn2S4under visible light, using air as the oxidant and a thiol as the initiator. It was proposed that the photogenerated holes over ZnIn2S4attack the thiol to produce thiyl radicals, which initiate the oxidative cleavage of the C=C bond in olefins to produce aldehydes/ketones. By further coupling with the condensation between the as-obtained aldehydes/ketones and alcohols, this strategy can also be applied to the production of different acetals directly from the olefins. This study demonstrates a new pathway to realize the oxidative cleavage of olefins to produce aldehydes/ketones, and also provides a new protocol for the production of acetals directly from the olefins.
Photochemical synthesis of acetals utilizing Schreiner's thiourea as the catalyst
Kokotos, Christoforos G.,Nikitas, Nikolaos F.,Spiliopoulou, Nikoleta
supporting information, p. 3539 - 3545 (2020/06/25)
Acetalization of aldehydes is an area of great importance in Organic Chemistry for both synthetic and biological puproses. Herein, we report a mild, inexpensive and green photochemical protocol, where Schreiner's thiourea (N,N′-bis[3,5-bis(trifluoromethyl)-phenyl]-thiourea) is utilized as the catalyst and cheap household lamps as the light source. A variety of aromatic and aliphatic aldehydes were converted into acetals in good to high yields (23 examples, 36-96% yield) and an example of the synthesis of a cyclic acetal is provided. The reaction mechanism was also studied.
