[80121-73-9]  · C7H15ISi  · 3-Iodo-2-trimethylsilylmethyl-1-propene  · (MW 254.21)

(a bifunctional conjunctive reagent that serves as a dipolar trimethylenemethane synthon;1,6 treatment with SnF2 affords a dianionic trimethylenemethane synthon9)

Physical Data: bp 25 °C/0.5 mmHg.2

Solubility: wide range of organic solvents.

Preparative Method: from the corresponding mesylate upon treatment with Sodium Iodide in acetone.2 The mesylate can be prepared from the commercially available alcohol.3

Purification: distillation in the dark (25 °C/0.5 mmHg, trap at -78 °C).2

Handling, Storage, and Precautions: can be stored in the dark at -20 °C for up to 3 months without significant deterioration.2

Dipolar Synthon for Trimethylenemethane.

The most common use of this reagent is as a 1,3-dipolar synthon for trimethylenemethane (TMM) (eq 1).1

The dipolar character is unmasked in two separate synthetic steps. In the first, the synthon reacts at the positive end upon treatment with a nucleophile such as an enolate or metalloenamine.2 In the second step, the nucleophilic end is unveiled, usually by treatment with fluoride ion. This nucleophile attacks the carbonyl or imine, completing the sequence. A similar reagent to the iodide, also a 1,3-dipolar synthon for TMM, is derived by treatment of the corresponding acetate with Pd0.1 The resulting 1,3-dipolar synthon differs from the iodide in several ways:

  • 1)one synthetic step is required to complete addition of the activated reagent;
  • 2)the reaction simulates a cycloaddition, with an electron deficient alkene as a reaction partner, rather than a carbonyl or imine;
  • 3)the nucleophilic end of the synthon reacts first, in contrast to the iodide.

    Reagent (1) has been used successfully with several classes of substrates.1,4,5 For example, ketone (2) was used in a synthesis employing the dipolar synthon as a means of annulating the third ring of the coriolin skeleton (eq 2).4

    Enone alkylation using (1), followed by Michael addition of the activated silane constitutes a second class of reactions employing this synthon.6 As shown in eq 3, the mode of addition in systems containing a second conjugated double bond can be controlled by changing the method used to activate the silane toward nucleophilic attack. Use of a Lewis acid favors 1,6-addition leading to seven-membered rings,6b,7 while treatment with fluoride ion favors 1,4-addition and formation of five-membered rings.6b

    Finally, imines can be used in the synthesis of nitrogen-containing heterocycles.8 One particularly interesting method involves a sequential photoexcitation-electron-transfer desilylation method for generating a diradical species capable of forming a spirocyclic product (eq 4).8c Notably, the ionic cyclization method involving fluoride ion leads, in this case, to mixtures of products including only small amounts (ca. 7%) of the desired spirocycle.8c

    Dianionic Synthon for Trimethylenemethane.9

    Reagent (1), upon metalation with Tin(II) Fluoride can be used as a dianionic synthon for trimethylenemethane (eq 5).10 This versatile synthon, in conjunction with bis-electrophiles such as (4), has been used to synthesize rings that range in size from five to eight members. An intramolecular hemiacetalization reaction followed by cyclization of the allylsilane makes possible the formation of seven- and eight-membered rings (eq 6).9b

    Related Reagents.


    1. Review of TMM and equivalents: Trost, B. M. AG(E) 1986, 25, 1.
    2. Trost, B. M.; Curran, D. P. TL 1981, 22, 5023.
    3. The alcohol can be prepared in two steps from 2-methyl-2-propen-1-ol: Trost, B. M.; Chan, D. M. T.; Nanninga, T. OS 1984, 62, 58.
    4. Trost, B. M.; Curran, D. P. JACS 1981, 103, 7380.
    5. Posner, G. H.; Asirvatham, E.; Hamill, T. G. JOC 1990, 55, 2132.
    6. (a) Majetich, G.; Desmond, R. W., Jr.; Soria, J. J. JOC 1986, 51, 1753. (b) Majetich, G; Hull, K.; Defauw, J.; Desmond, R. TL 1985, 26, 2747. (c) Majetich, G.; Desmond, R.; Casares, A. M. TL 1983, 24, 1913.
    7. Majetich, G.; Leigh, A. J.; Condon, S. TL 1991, 32, 605.
    8. (a) Gelas-Mialhe, Y.; Gramain, J.-C.; Hajouji, H.; Remuson, R. H 1992, 34, 37. (b) Bell, T. W.; Hu, L.-Y. TL 1988, 29, 4819. (c) Ahmed-Schofield, R.; Mariano, P. S. JOC 1985, 50, 5667.
    9. (a) Molander, G. A.; Shubert, D. C. JACS 1987, 109, 576. (b) Molander, G. A.; Shubert, D. C. JACS 1987, 109, 6877. (c) Molander, G. A.; Shubert, D. C. JACS 1986, 108, 4683.
    10. For other dianion TMM synthons, see: (a) Molander, G. A.; Shubert, D. C. TL 1986, 27, 787. (b) Jones, M. D.; Kemmitt, R. D. W. CC 1985, 811.

    Therese M. Bregant & R. Daniel Little

    University of California, Santa Barbara, CA, USA

    Copyright 1995-2000 by John Wiley & Sons, Ltd. All rights reserved.