Halogenation of Fluorinated 1,3,5‐Triketones

Abstract

The behavior of linear and cyclic fluorinated 1,3,5-triketones and their metal derivatives towards common halogenating agents was examined, and optimal reaction conditions for the straightforward synthesis of mono-, di-, and tetrahalogenated products were found (Schemes 1 -3). An aromatization through a double HBr elimination from an a,a'-dibrominated cyclohexanone was shown to be a promising synthetic route to 1,1'-(2-hydroxy-1,3-phenylene)bis[2,2,2-trifluoroethanones] (= 2,6-bis(trifluoro-A C H T U N G T R E N N U N G acetyl)phenols; Scheme 4). Additionally, the 1,3,5-triketones prepared add readily H 2 O or alcohols to produce novel bridged 2,6-dihydroxypyran-4-ones (Scheme 2). The structure of the obtained compounds 6a and 7a was confirmed by X-ray structure analysis.

Reactions of fluoroalkyl-containing lithium 1,3-diketonates with diaminoarenes and 2-aminobenzenethiol

“…19 Triketonate 7 was described in the study. 22 The course of the reactions was monitored by TLC (Silufol UV 254, CHCl 3 as the eluent). The visualization of the spots was performed with the use of aqueous KMnO 4 solutions.…”

Aromatization via a Dibromination-Double Dehydrobromination Sequence: A Facile and Convenient Synthetic Route to 2,6-Bis(trifluoroacetyl)phenols

“…With these results in hand and using the principles established earlier, 11 we were able to synthesize a range of phenol derivatives 3 with various substituents in the 4position, starting from commercially available cyclohexanones. The corresponding synthetic sequence is depicted in Table 2.…”

“…10 Indeed, in the course of recent work we observed that the 2,4-dibrominated 1,3,5triketone 4b underwent double dehydrobromination under basic conditions to afford phenol 3b in 31% isolated yield ( Table 1, entry 1). 11 Given the ease of the preparation of both compound 4b and its precursor 2,6-bis(trifluoroacetyl)cyclohexanone (5b, Table 2), 12 we became interested to know whether related reactions could be developed into a general method to synthesize the target 2,6-bis(trifluoroacetyl)phenols 3 ( Table 2). Attempts to directly convert 5b into 3b when conventional oxidants such as elemental sulfur or 2,3-dichloro-5,6-dicyano-1,4benzoquinone were used failed.…”

“…Double Claisen condensation with ethyl trifluoroacetate and with lithium hydride as the base provided the corresponding 1,3,5-triketones 5 in 70-90% yields ( Table 2, step i). Treatment of 5 with excess elemental bromine furnished compounds 4 ( Table 2, step ii), 11 which could be dehydrobrominated readily without isolation (step iii). This formal oxidation, or rather two-step aromatization of 5, allowed the preparation of phenol derivatives 3 in a simple and convenient one-pot procedure in 51-95% yields (Table 2).…”

“…Since only complex reaction mixtures 14 formed when we tried to aromatize compound 5g (Table 2), we sought to prepare acid 3g from ester 3f (Table 3). Potassium bicar- a Starting compound 4b was pre-generated from 5b, 11 and converted into 3b without isolation.…”