An Intriguing Hydroiodination of Alkenes and Alkynes with Titanium Tetraiodide

Abstract

Olefins and acetylenes were hydroiodinated with titanium tetraiodide to give alkyl iodides, vinyl iodides, and alkyl diiodides in good yields. In the presence of acetals, the reaction gave intriguing C-C bond-forming products.

titanium tetraiodide - hydroiodination - alkene - alkyne - Prins reaction - alkyl iodide - alkyl diiodide

References

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<A NAME="RU19905ST-3">3</A>

A typical procedure is as follows: To a suspension of TiI₄ (Soekawa Chemical Co., used after sublimation, [2a] 111 mg, 0.20 mmol) in CH₂Cl₂ (1.0 mL) was added a solution of cyclododecene (33.3 mg, 0.20 mmol) in CH₂Cl₂ (1.0 mL) at r.t. After stirring at r.t. for 12 h, the reaction was quenched by the addition of sat. aq NaHCO₃ and aq NaHSO₃ (5%). The mixture was filtered through a Celite pad. The layers were separated and the aqueous layer was extracted with EtOAc (3 × 10 mL). The combined organic extracts were washed with sat. aq NaHCO₃ and brine, and then dried over anhyd Na₂SO₄. Purification by silica gel TLC (hexane) gave iodocyclododecane (53.8 mg, 91%) as a colorless oil.

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The reaction of phenylacetylene with TiI₄ at low temperatures sometimes gave diiodinated product of type 6 (R = Ph) in the crude reaction mixture. Upon standing at room temperature, this product underwent dehydroiodination to give the vinyl iodide 5.

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<A NAME="RU19905ST-8">8</A>

We have carried out several experiments quenching the reaction mixtures derived from alkenes or alkynes and TiI₄ with D₂O. However, little or no deuterium incorporation was observed.
The reaction in CD₂Cl₂ also did not give the deuteriated product (vide supra). Elucidation of the intermediary species will be reported in due course.