Iodosylbenzene-Boron Trifluoride1

PhIO.BF3
(PhIO)

[536-80-1]  · C6H5IO  · Iodosylbenzene-Boron Trifluoride  · (MW 220.01) (PhIO.BF3)

[108208-48-6]  · C6H5BF3IO  · Iodosylbenzene-Boron Trifluoride  · (MW 287.82)

(iodonium-transfer reagent to alkenyl-2a and alkynylsilanes;2b oxidizing agent for silyl enol ethers3)

Physical Data: PhIO: mp 210 °C (dec).

Solubility: PhIO is a polymer, linked by I-O-I bonds. Therefore it is insoluble in most organic solvents. Upon dissolution in acetic acid and methanol, it is known to react to form (diacetoxyiodo)benzene and (dimethoxyiodo)benzene, respectively.10

Form Supplied in: PhIO is a pale yellow solid. Some commercial compounds are contaminated with iodyl benzene (PhIO2: colorless solid).

Analysis of Reagent Purity: iodometric titration.

Preparative Method: see Salzman and Sharefkin.11

Handling, Storage, and Precautions: PhIO decomposes explosively if heated to 210 °C. The solid gradually disproportionates to iodobenzene and iodyl benzene at rt and must be stored at -20 °C.

Iodosylbenzene is activated by coordination of Boron Trifluoride Etherate to the oxygen atom, presumably via the formation of the highly electrophilic species C6H5Id+-OBF3d-.2 This species undergoes an iodonium-transfer reaction, which makes possible the synthesis of alkenyl- and alkynyl(phenyl)iodonium salts. Because of the superleaving ability of the phenyliodonium group, alkenyliodonium salts serve as the progenitors for generating alkylidenecarbenes via base-induced a-elimination under mild conditions (eq 1)4 and as the highly activated species of alkenyl halides in nucleophilic vinylic substitutions (eq 2).2a Nucleophilic vinyl substitutions of (E)-alkenyliodonium salts with n-Bu4NX proceed with exclusive inversion of configuration.5 Tandem Michael-carbene insertion reactions of alkynyl(phenyl)iodonium salts provide a useful tool for the synthesis of cyclopentenes (eq 3) and furans.6

Treatment of propargylsilanes, -germanes, and -stannanes with iodosylbenzene-BF3 promotes a reductive iodonio-Claisen rearrangement under mild conditions, yielding o-propargyliodoarenes (eq 4).7 Intermediate allenyl(phenyl)iodinanes are involved in this reaction.

Carbon-tin bond cleavage by iodosylbenzene-BF3 makes possible the conversion of trimethylstannyl groups into hydroxy groups with retention of stereochemistry and the stereoselective osmylation of alkenes utilizing an intramolecular hypervalent tin-oxygen interaction.8 Oxidative Grob fragmentation of g-stannyl alcohols gives unsaturated carbonyl compounds and lactones (eq 5).9

Oxidation of silyl enol ethers gives a-hydroxy and a-methoxy ketones (eq 6).3


1. (a) Koser, G. F. The Chemistry of Functional Groups, Supplement D; Wiley: New York, 1983; Chapters 18, 25. (b) Ochiai, M. Rev. Heteroatom Chem. 1989, 2, 92. (c) Moriarty, R. M.; Prakash, O. ACR 1986, 19, 244.
2. (a) Ochiai, M.; Sumi, K.; Takaoka, Y.; Kunishima, M.; Nagao, Y.; Shiro, M.; Fujita, E. T 1988, 44, 4095. (b) Ochiai, M.; Kunishima, M.; Sumi, K.; Nagao, Y.; Fujita, E. TL 1985, 26, 4501. (c) Ochiai, M.; Ito, T.; Takaoka, Y.; Masaki, Y.; Kunishima, M.; Tani, S.; Nagao, Y. CC 1990, 118.
3. (a) Moriarty, R. M.; Duncan, M. P.; Prakash, O. JCS(P1) 1987, 1781. (b) Moriarty, R. M.; Prakash, O.; Duncan, M. P.; Vaid, R. K.; Musallam, H. A. JOC 1987, 52, 150.
4. (a) Ochiai, M.; Takaoka, Y.; Nagao, Y. JACS 1988, 110, 6565. (b) Ochiai, M.; Kunishima, M.; Tani, S.; Nagao, Y. JACS 1991, 113, 3135. (c) Ochiai, M.; Uemura, K.; Masaki, Y. JACS 1993, 115, 2528.
5. Ochiai, M.; Oshima, K.; Masaki, Y. JACS 1991, 113, 7059.
6. Ochiai, M.; Kunishima, M.; Nagao, Y.; Fuji, K.; Shiro, M.; Fujita, E. JACS 1986, 108, 8281.
7. (a) Ochiai, M.; Ito, T.; Takaoka, Y.; Masaki, Y. JACS 1991, 113, 1319. (b) Gately, D. A.; Luther, T. A.; Norton, J. R.; Miller, M. M.; Anderson, O. P. JOC 1992, 57, 6496.
8. Ochiai, M.; Iwaki, S.; Ukita, T.; Matsuura, Y.; Shiro, M.; Nagao, Y. JACS 1988, 110, 4606.
9. (a) Ochiai, M.; Ukita, T.; Iwaki, S. M.; Nagao, Y.; Fujita, E. JOC 1989, 54, 4832. (b) Ochiai, M.; Iwaki, S.; Ukita, T.; Nagao, Y. CL 1987, 133.
10. Schardt, B. C.; Hill, C. L. IC 1983, 22, 1563.
11. Saltzman, H.; Sharefkin, J. G. OSC 1973, 5, 658.

Masahito Ochiai

University of Tokushima, Japan



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