[78199-88-9] · C6H11ISi · 3-Iodo-1-trimethylsilylpropyne · (MW 238.16)
(addition to aldehydes in the presence of tin(II) chloride or metallic tin and aluminum to provide a-hydroxyallenes and b-alkynic alcohols; propargylic alkylating agent)
Alternate Name: (3-iodo-1-propynyl)trimethylsilane; trimethylsilylpropargyl iodide.
Physical Data: bp 42 °C/2 mmHg.
Solubility: typical reaction solvents are DMF, dichloromethane, THF.
Analysis of Reagent Purity: 1H NMR.1
Preparative Methods: from Iodine and [3-(trimethylsilyl)-2-propynyl]-o-phenylene phosphite in dichloromethane (52%), or iodine and 3-(trimethylsilyl)-2-propyn-1-ol and Tri-n-butylphosphine (47%);1 from trimethylsilylpropargyl bromide and Sodium Iodide;2 by treatment of trimethyl(2-propynyl)stannane with Ethylmagnesium Bromide, Bromotrimethylsilane in THF followed by I2 in CCl4 (65-70%).3
Handling, Storage, and Precautions: the distilled trimethylsilylpropargyl iodide was found by 1H NMR to have decomposed to the extent of 20% after 5 d at -10 °C in the dark.1 Care should be taken when working with the tin derivative. Organostannane reagents are highly toxic and readily absorbed through the skin. Proper safety equipment (i.e. fume hood, gloves, protective eyewear) should be utilized when handling the organostannane derivative.4
Considerable attention has been focused on the control of regioselectivity in the addition of allenic and propargylic organometallic reagents to carbonyl compounds. Mukaiyama and Harada have found that the addition of trimethylsilylpropargyl iodide to aldehydes in a DMF/1,3-Dimethyl-2-imidazolidinone (DMI) mixture in the presence of Tin(II) Chloride results in the formation predominantly of the a-hydroxy allenes (a-allenic alcohols) (eq 1).2
In a complimentary study, Nokami et al. found that trimethylsilylpropargyl iodide reacts with metallic Tin in the presence of metallic Aluminum to give bis(trimethylsilylpropargyl)tin diiodide. This then reacts with aldehydes to give either a-allenic or b-alkynic alcohols (homopropargyl alcohols) selectively, depending on the choice of solvent (eq 2).5
Analogous additions to aldehydes and ketones with metallated derivatives of 3-bromo-1-trimethylsilylpropyne (which is commercially available) are also known. Either a-allenic6 or b-alkynic alcohols7 may be obtained selectively by using the appropriate metal derivative. The organolithium species prepared from 1-trimethylsilylpropyne has also been utilized.8
3-Iodo-1-trimethylsilylpropyne has been used in the trapping of enolates generated in 1,4-additions of organometallic reagents to 2-cyclopentenone derivatives.1 Noyori et al. used this reaction in the three-component coupling synthesis of prostaglandins (eq 3).9 Reaction of trimethylsilylpropargyl iodide with an alkynic Grignard reagent in the presence of Copper(I) Cyanide has also been demonstrated in the synthesis of a preclavulone A model (eq 4).10
3-Bromo-1-trimethylsilylpropyne has also been used as an alkylating agent for trapping enolates and other carbanions.11 It has also been used in the preparation of alkynic ylides.12
Carol K. Wada
Indiana University, Bloomington, IN, USA