[124897-71-8]  · C7H15GeI  · 4-Iodo-2-trimethylgermyl-1-butene  · (MW 298.71)

(precursor of lithium (3-trimethylgermyl-3-butenyl)cyanocuprate, a synthetically useful reagent for effecting annulation reactions1-3)

Alternate Name: 3-iodo-1-methylenepropyltrimethylgermane.

Physical Data: colorless liquid; distillation temperature (bulb-to-bulb) 85-92 °C/15 mmHg.

Solubility: sol THF, CHCl3.

Preparative Methods: from 4-chloro-2-lithio-1-butene (1) (see 4-Chloro-2-trimethylstannyl-1-butene) and from 1-trimethylsilyl-4-trimethylsilyloxy-1-butyne (3), as shown in eqs 1 and 2, respectively.1,5 Of these two methods, the latter is experimentally more convenient and is also less expensive.

Handling, Storage, and Precautions: organogermanium compounds4 and alkyl iodides are toxic and, therefore, the reagent should be prepared, distilled, and used in a fume hood. When stored in a freezer over copper wire under an inert atmosphere, the reagent is stable indefinitely. Should be distilled just prior to use; reactions should be carried out using dry THF and an inert atmosphere.

Annulation Methods.

The title reagent (2), upon sequential treatment with t-Butyllithium and Copper(I) Cyanide, is readily converted into the structurally novel lower order heterocuprate (4) (eq 3).1,2 The latter species has been employed in the development of the new, synthetically valuable annulation sequences outlined below.

Conjugate addition of (4) to the enone (5) affords the keto vinylgermane (6), which upon treatment with Iodine is transformed into the corresponding vinyl iodide (7) (eq 4).1 Reaction of (7) with n-Butyllithium in THF provides, highly stereoselectively, the alkene alcohol (8), which serves as a suitable intermediate for the total synthesis of the isolabdane diterpenoid ambliol B (9).1

Reagent (4) has also found effective use in the development of a methylenecyclopentane annulation method shown in general terms by the conversion of (10) into (11).2 This annulation process is regioisomeric with respect to the transformation of (10) into (12) (eq 5)6 (see also 4-Chloro-2-trimethylstannyl-1-butene).

A specific example of the new method is shown in eq (6).2 Conjugate addition of reagent (4) to (R)-(-)-carvone (13) provides (14), which is readily converted into (15). In the key step, the keto iodide (15) is treated with base in the presence of Tetrakis(triphenylphosphine)palladium(0) to afford the annulation product (16). Structures (17) and (18) represent likely intermediates in the reaction pathway of this novel cyclization process.2

When the a,b-unsaturated ketone substrate contains an a-proton in place of an a-alkyl group, the initially formed annulation product (b,g-unsaturated ketone) isomerizes under the basic reaction conditions to the corresponding a,b-unsaturated ketone (eq 7).2

This new annulation method played an important role in a total synthesis of the tetraquinane diterpenoid crinipellin B (19) (eq 8).3

1. Piers, E.; Marais, P. C. CC 1989, 1222.
2. Piers, E.; Marais, P. C. JOC 1990, 55, 3454.
3. Piers, E.; Renaud, J. JOC 1993, 58, 11.
4. Schauss, A. G. Biol. Trace Elem. Res. 1991, 29, 267.
5. Piers, E.; Lemieux, R. JCS(P1) 1995, 3.
6. (a) Piers, E.; Karunaratne, V. T 1989, 45, 1089. (b) Piers, E.; Renaud, J. S 1992, 74.

Edward Piers & Christine Rogers

University of British Columbia, Vancouver, BC, Canada

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