Expanding the scope of methyl xanthate esters - From Barton-McCombie reaction auxiliary to versatile protective group
作者:Karin Thorsheim、Sophie Manner、Ulf Ellervik
DOI:10.1016/j.tet.2017.09.022
日期:2017.11
presented as a versatile protective group for alcohols. Hydroxyl groups can easily be transformed into methyl xanthate esters by several methods and are commonly used as an auxiliary in the Barton-McCombiereaction. We show that these methyl xanthate esters can readily and chemoselectively be cleaved under mild conditions by the action of diethylenetriamine using microwave heating. This method is orthogonal
mechanism is proposed to proceed via a cyclic dioxolane‐type intermediate, formed between the iron(III) species and two adjacent hydroxyl groups. This approach represents the first transition‐metal catalysts that are able to replace stoichiometric amounts of organotin reagents in regioselectivealkylation. The reactions generally lead to very high regioselectivities and high yields, on par with, or better
An efficient one‐pot method for the selective benzylation of diols and polyols using 0.1 equiv. of organotin reagents and tetrabutylammonium bromide as catalyst has been developed. The diols and polyols containing a cis‐vicinal diol were regioselectively benzylated in 70–94% isolated yields. A catalytic reaction mechanism was also proposed.
Highly Efficient Selective Benzylation of Carbohydrates Catalyzed by Iron(III) with Silver Oxide and Bromide Anion as Co-catalysts
作者:Bo Ren、Jian Lv、Yu Zhang、Jun Tian、Hai Dong
DOI:10.1002/cctc.201601558
日期:2017.3.20
and polyols was developed. With the use of Ag2O (0.6 equiv.) and tetrabutylammonium bromide (0.1 equiv.) as co‐catalysts, the iron(III)‐catalyzed benzylation reaction proceeded to completion at 40 °C within 2–3 h and gave the products in high yields with high regioselectivities. A mechanism involving the principle of enhancedbasicity of Ag2O by softanions was proposed.
approach to regioselectivebenzylation of carbohydrate trans-diols was developed, where 0.1 equiv. of Bu2SnCl2 and 0.1 equiv. of TBABr were used as the catalysts and 2.0 equiv. of BnCl was used as the benzylationreagent. In most cases, similar or better benzylationregioselectivities and isolated yields were obtained by using catalyticamounts of Bu2SnCl2, rather than stoichiometric amounts of organotin