Development of fluorination methods using continuous-flow microreactors
作者:Marcus Baumann、Ian R. Baxendale、Laetitia J. Martin、Steven V. Ley
DOI:10.1016/j.tet.2009.05.083
日期:2009.8
The safe and reliable use of various fluorination methods including nucleophilic fluorination (DAST), trifluoromethylation (Ruppert's reagent) and electrophilic fluorination (Selectfluor®) in a continuous-flow microreactor is reported. Special attention was given to the use of in-line scavenging procedures in order to obtain clean products without the need for further purification.
Primary and secondary alcohols are efficiently converted to the corresponding alkyl halidesunderneutralconditions.
伯醇和仲醇在中性条件下可有效地转化为相应的烷基卤。
Iridium-Catalyzed Allylic Fluorination of Trichloroacetimidates
作者:Joseph J. Topczewski、Timothy J. Tewson、Hien M. Nguyen
DOI:10.1021/ja2087213
日期:2011.12.7
allylic fluorination method utilizing trichloroacetimidates in conjunction with an iridium catalyst has been developed. The reaction is conducted at room temperature under ambient air and relies on Et(3)N·3HF reagent to provide branched allylic fluorides with complete regioselectivity. This high-yielding reaction can be conducted on a multigram scale and shows considerable functional group tolerance
Diethylaminodifluorosulfinium tetrafluoroborate (XtalFluor-E) and morpholinodifluorosulfinium tetrafluoroborate (XtalFluor-M) are crystalline fluorinating agents that are more easily handled and significantly more stable than Deoxo-Fluor, DAST, and their analogues. These reagents can be prepared in a safer and more cost-efficient manner by avoiding the laborious and hazardous distillation of dialkylaminosulfur trifluorides. Unlike DAST, Deoxo-Fluor, and Fluolead, XtalFluor reagents do not generate highly corrosive free-H F and therefore can be used in standard borosilicate vessels. When used in conjunction with promoters such as Et3N center dot 3HF, Et3N center dot 2HF, or DBU, XtalFluor reagents effectively convert alcohols to alkyl fluorides and carbonyls to gem-difluorides. These reagents are typically more selective than DAST and Deoxo-Fluor and exhibit superior performance by providing significantly less elimination side products.
Synthesis of α-trifluoromethylated amides by Eschenmoser–Claisen-type rearrangement of allylic alcohols
A new, mild method to prepare alpha-trifluoromethylated amides bearing an additional trans-configured double bond in gamma-position is described. Treatment at room temperature of fluorinated and non-fluorinated allylic alcohols 1 and 2 with the 1,1,3,3,3-pentafluoropropene-diethylamine adduct (PFPDEA) in the presence of triethylamine as base gave the products of [3,3]-sigmatropic Eschenmoser-Claisen-type rearrangements with good yields and excellent diastereoselectivity due to chair-like conformations of transition states. Starting with enantiomerically enriched allylic alcohols chirality transfer from carbon 3 of the allylic system to carbon 2 of the final alpha-trifluoromethyl carboxamides was observed. This methodology was applied to both simple and more complex, including terpenic, allylic alcohols and might be developed to an alternative strategy to the well-known electrophilic alpha-trifluoromethylation of carbonyl compounds. (C) 2012 Elsevier B.V. All rights reserved.