2-Methyl-1-propenyl Trifluoromethanesulfonate

[53282-30-7]  · C5H7F3O3S  · 2-Methyl-1-propenyl Trifluoromethanesulfonate  · (MW 204.19)

(precursor to dimethylvinylidene carbene,1 2-methyl-1-propenyl ethers,1 isopropylidenecyclopropanes,2 isopropylidenecyclopropenes,2 3-isopropylindazoles,3 and 2-methyl-1-propenyltriphenylphosphonium triflates4)

Physical Data: bp 65-66 °C/70 mmHg.

Solubility: sol most organic solvents.

Preparative Method: prepared in a single step from 2-methylpropionaldehyde, Trifluoromethanesulfonic Anhydride, and a hindered pyridine in 1,2-dichloroethane at reflux (eq 1). Distillation gives the product in 45% yield.5

General Discussion.

This reagent is quantitatively converted to the electrophilic carbene (2) (eq 2) on treatment with Potassium t-Butoxide.1 This carbene readily inserts into an oxygen-hydrogen bond, and thus reacts with t-butanol to give ether (3) (eq 3).1

Carbene (2) reacts normally with a variety of substrates. When an alkene is used as solvent (eqs 4 and 5), the corresponding isopropylidenecyclopropanes are generated in good to excellent yield.1 The silicon-hydrogen bond is an efficient trap (eq 6); the reaction proceeds with retention of configuration at silicon.6

Alkynes react with (2) to yield isopropylidenecyclopropenes (4) (eq 7).2 These products cannot be isolated, but will undergo a facile Diels-Alder reaction. Alternatively, protonation of the product gives isopropylcyclopropenium ions.

Reaction of (1) in the presence of azoarenes yields the unusual 3-isopropylindazoles (eq 8), presumably via an isopropylidenediaziridine.3 In the presence of Triphenylphosphine, a palladium catalyst converts (1) into the corresponding phosphonium salt in good yield (eq 9).4

1. Stang, P. J.; Mangum, M. G.; Fox, D. P.; Haak, P. JACS 1974, 96, 4562.
2. Stang, P. J.; Mangum, M. G. JACS 1975, 97, 3854.
3. Krageloh, K.; Anderson, G. H.; Stang, P. J. JACS 1984, 106, 6015.
4. Hinkle, R. J.; Stang, P. J.; Kowalski, M. H. JOC 1990, 55, 5033.
5. Stang, P. J.; Treptow, W. S 1980, 283.
6. Stang, P. J.; Learned, A. E. JACS 1987, 109, 5019.

Scott McN. Sieburth & Louis Fensterbank

State University of New York at Stony Brook, NY, USA

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