Stereoselective synthesis of 4-fluoro-1,3-alkadienylboronates and their application in the stereoselective synthesis of fluoropolyenes

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Abstract

(1E,3E)- and (1E,3Z)-4-fluoro-1,3-alkadienylboronates were stereoselectively prepared by the Heck-reaction of a vinylboronate with (E)- or (Z)-2-fluoro-1-alkenyliodonium salts, and applied to the Suzuki–Miyaura coupling reaction for the synthesis of fluoropolyenes.

Introduction

Polyene natural products that exhibit significant bioactivities are widely known in nature [1], [2]. The fluorinated analogs of the polyene are of great interest for studying their actions in vivo and the modification of their activities [3], [4], [5], [6], [7], [8]. Fluorodienylmetals (1) are effective as building blocks for the synthesis of polyene analogs with fluorine attached to the double bonds [5], [8]. Although fluorodienylboronates (1, M = B in Scheme 1) can be used as building blocks for the synthesis of various fluoropolyenes by the Suzuki–Miyaura coupling reaction [9], they have not yet been synthesized.

Alkadienylboronates are synthesized by the Heck-reaction of vinylboronates (4) with haloalkenes and used for polyene synthesis [10], [11]. Recently, we succeeded in the stereoselective synthesis of (E)- and (Z)-2-fluoro-1-iodoalkenes (2) and 2-fluoroalkenyliodonium salts (3) [12], [13], [14]. For the synthesis of fluoroalkadienylboronates (5) and their application in the synthesis of fluoropolyenes (6), we examined the Heck-reaction of vinylboronates (4) with 2-fluoro-1-iodoalkenes 2 and 2-fluoroalkenyliodonium salts 3 (Scheme 2).

Section snippets

Result and discussion

In the Heck-reaction of the vinylboronates with haloalkenes, the Suzuki–Miyaura coupling reaction competes to give dienes and the yield of the desired dienylboronates decreases [10]. Recently, Whiting co-workers successfully depressed the undesired Suzuki–Miyaura coupling using 4,4,6-trimethyl-2-vinyl-1,3,2-dioxaborinane as the vinylboronate and performing the reaction at a high temperature [11]. However, under the same conditions, the Heck-reaction of (E)-2-fluoro-1-iodoalkenes (2) with

Conclusion

In conclusion, various (1E,3E)- and (1E,3Z)-4-fluoro-1,3-alkadienylboronates were stereoselectively prepared by the Heck-reaction of 4,4,5,5-tetramethyl-2-vinyl-[1,3,2]-dioxaborolane with (E)- or (Z)-2-fluoro-1-alkenyliodonium salts. The reaction proceeded at room temperature and the pure fluoroalkadienylboronates were isolated by column chromatography. The resulting fluoroalkadienylboronates can be used for the synthesis of fluoropolyenes by the Suzuki–Miyaura coupling reaction with aryl or

General methods

The IR spectra were recorded using a JASCO FT/IR-410 spectrophotometer. The 1H NMR (400 MHz) spectra, 19F NMR (376 MHz) spectra and 13C NMR (100 MHz) spectra were recorded in CDCl3 on a JEOL JNM-A400II FT NMR spectrometer and the chemical shift, δ, are referred to TMS (1H, 13C) and CFCl3 (19F), respectively. The EI-high-resolution mass spectra were measured on a JEOL JMS-700TZ spectrometer.

(E)-2-Fluoroalkenyliodonium salts 3ae was prepared from the corresponding alkynes and iodotoluene difluoride

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