New approach to α-pentafluorosulfanyl-substituted carboxylic acid derivatives via Ireland-Claisen rearrangements

Syn-selective silicon Mukaiyama-type aldol reactions of (pentafluoro-λ6-sulfanyl)acetic acid esters with aldehydes

“…Considering our earlier results [ 31 ] on TMSOTf-mediated Claisen-type rearrangements of SF 5 -acetates of allyl alcohols, we favor the initial formation of ( Z )-enolates (ketene silylacetals) 5 in the aldol reactions ( Scheme 2 ).…”

“…Recently, we discovered that silylated enolates can be formed as mixtures of ( E )- and ( Z )-isomers from SF 5 -substituted acetic acid esters of aliphatic terminal allylic alcohols at low temperature. At slightly elevated temperature, the latter diastereomers are transformed to γ,δ-unsaturated α-pentafluoro-λ 6 -sulfanyl alkanoic acids in an Ireland–Claisen rearrangement [ 31 ]. Under slightly modified conditions, this type of rearrangement was also successful for SF 5 -substituted acetic esters of cinnamyl alcohols [ 32 ].…”

Synthesis of Monofluoroalkenes: A Leap Forward

“…In 2014, the Haufe group developed an Ireland-Claisen rearrangement to access fluoroalkene-containing α-(pentafluorosulfanyl)-substituted carboxylic acid derivatives (Scheme 148). 155 A series of (pentafluorosulfanyl)acetic acid esters were prepared; they underwent the Ireland-Claisen rearrangement under mild conditions, with Et 3 N as a base and TMSOTf as silylating agent to give (Z)-monofluoroalkenes in good yields and with excellent selectivity. In 2017, the Haufe group reported that the order of addition of the reagents (i.e., Et 3 N before TMSOTf) was important to increase the yields.…”

Synform Issue 2016/6

“…We have been able to successfully use it in the preparation of α-SF 5 carboxylic acid derivatives by Ireland-Claisen rearrangements of allylic SF 5 acetates," continued Professor Haufe, who added: "For the first time, intermediately formed SF 5 -substituted Literature Coverage Synform silicon enolates were established by low-temperature NMR spectroscopy. 7 This observation led us to speculate whether enolates of alkyl SF 5 acetates might be useful in aldol reactions. "…”