Preparation of trifluoroethyl- and phenyl-protected sulfates using sulfuryl imidazolium salts
摘要:
Sulfuryl imidazolium salts (SIS's), a new class of sulfating agents, were prepared bearing the trifluoroethyl (TFE) and phenyl groups, two functionalities that have been used for the protection of sulfate monoesters, by subjecting the corresponding sulfonyl imidazoles with methyl triflate. In contrast, SIS's bearing the electron donating neopentyl and isobutyl groups, two moieties that have also been used for the protection of sulfates, were found to be unstable and could not be isolated though SIS's bearing electron donating aryl groups, such as a p-methoxyphenyl or p-thiomethylphenyl group were readily prepared and are stable compounds. In most instances, TFE-protected phenolic and carbohydrate sulfates were obtained in good yield by reaction of the corresponding SIS's with steroids and carbohydrates. Phenyl-protected carbohydrates were also readily prepared using the corresponding SIS's. Those SIS's having a methyl group at the 2-position of the imidazole ring were, in general, superior sulfating agents to those, which lacked a methyl group at this position. The use of SIS's to prepare TFE-protected sulfates represents a significant improvement of the previous reported procedure, which involved treating unprotected sulfates with trifluorodiazoethane. The TFE protecting group was removed from steroidal sulfates and secondary sulfates in carbohydrates in high yields using NaN(3) in warm DMF, conditions that are less vigorous than those previously reported for removing this group. Deprotection of TFE-protected 6-sulfated carbohydrates using NaN3 in warm DMF proceeded in lower yields due to partial desulfation. (C) 2010 Elsevier Ltd. All rights reserved.
Palladium- and Nickel-Catalyzed Aminations of Aryl Imidazolylsulfonates and Sulfamates
作者:Lutz Ackermann、René Sandmann、Weifeng Song
DOI:10.1021/ol200267b
日期:2011.4.1
A nickel complex derived from dppf, along with NaOt-Bu as the base, allowed for challenging aminations of aryl sulfamates. An improved functional group tolerance is observed in novel palladium-catalyzed aminations of imidazolylsulfonates with rac-BINAP as the ligand.
衍生自dppf的镍络合物以及NaO t -Bu作为碱,可实现富挑战性的氨基磺酸氨基酯的胺化反应。以rac -BINAP为配体的新型钯催化的咪唑基磺酸盐胺化反应观察到官能团耐受性提高。
Palladium-Catalyzed Mono-α-Arylation of Acetone with Aryl Imidazolylsulfonates
作者:Lutz Ackermann、Vaibhav P. Mehta
DOI:10.1002/chem.201201394
日期:2012.8.13
Set the ace(tone): A palladium catalyst derived from the bidentate XantPhos ligand and Pd(OAc)2 has enabled broadly applicable mono‐α‐arylations of acetone to be performed with air‐ and moisture‐stable arylimidazolylsulfonates as most user‐friendly electrophiles (see scheme).
A catalytic system comprised of Pd(OAc)2 and bidentate ligand dppe enabled first direct arylations with moisture-stable aryl sulfamates as electrophiles, and proved applicable to unprecedented C−H bond functionalizations with easily accessible alkenyl phosphates as well as benzyl phosphates.
Phosphane-free Suzuki–Miyaura Coupling of Aryl Imidazolesulfonates with Arylboronic Acids and Potassium Aryltrifluoroborates under Aqueous Conditions
作者:José Francisco Cívicos、Mohammad Gholinejad、Diego A. Alonso、Carmen Nájera
DOI:10.1246/cl.2011.907
日期:2011.9.5
Aryl imidazole-1-sulfonates are efficiently cross-coupled with arylboronic acids and potassium aryltrifluoroborates using only 0.5 mol % of oxime palladacycles 1 under aqueous conditions at 110 °C. Under these simple phosphane-free reaction conditions a wide array of biaryl derivatives has been prepared in high yields. This methodology allows in situ phenol sulfonation and one-pot Suzuki arylation as well as the employment of microwave irradiation conditions.
Oxime-Palladacycle-Catalyzed Suzuki-Miyaura Arylation and Alkenylation of Aryl Imidazolesulfonates under Aqueous and Phosphane-Free Conditions
作者:José Francisco Cívicos、Diego A. Alonso、Carmen Nájera
DOI:10.1002/ejoc.201200368
日期:2012.7
Aryl and hetaroaryl imidazole-1-sulfonates are efficiently arylated and alkenylated with aryl- and alkenylboronic acids and potassium trifluoroborates by using 0.5 mol-% palladacycles 1 or Pd(OAc)2 at 110 °C under aqueous and phosphane-free conditions. Reactions can be performed by using conventional or microwave heating, leading to biaryls, stilbenes, and alkenylarenes in good to high yields, and