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Synlett 2006(14): 2187-2190  
DOI: 10.1055/s-2006-949612
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Simple Procedure for the Synthesis of Functionalized 1,3-Butadienes and Cyclopentenones from Fischer Carbene Complexes

Francisco J. Fañanás*, Jorge Alonso, Félix Rodríguez
Instituto Universitario de Química Organometálica ‘Enrique Moles’, Unidad Asociada al C.S.I.C., Universidad de Oviedo, Julián Clavería 8, 33006 Oviedo, Spain
Fax: +34(98)5103446; e-Mail: fjfv@uniovi.es;
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Publication History

Received 2 June 2006
Publication Date:
24 August 2006 (online)

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Abstract

Consecutive treatment of alkenyl carbene complexes with lithium enolates derived from methyl ketones and iodine leads to functionalized 1,3-butadiene derivatives containing both electron-donating and electron-withdrawing groups. Functionalized bicyclic cyclopentenones are easily available by sequential treatment of dihydropyranyl carbene complexes with lithium enolates, iodine, and catalytic amounts of copper(II) triflate.

Key words

carbene complexes - iodine - ketones - organometallic reagents - transition metals

    References and Notes

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7

Alternatively, compound 4 could be formed by the reaction of 5 with iodine through an SE2′ mechanism followed by a γ-elimination.

8

The diisopropylamine comes from the generation of lithium enolates 3 with LDA.

9

Cyclopentenone Derivatives 8; General Procedure To a THF (10 mL) solution of LDA (0.5 mmol) at -30 °C was added the corresponding ketone (0.5 mmol) to generate enolate 3. After 30 min the solution was cooled to -50 °C and then the carbene complex 2a (0.5 mmol), dissolved in THF (5 mL), was added slowly dropwise. After 10 min I2 (0.5 mmol) was added and the temperature was allowed to rise to r.t. slowly (3 h). The solvents were removed and the residue was filtered through a very short plug of silica (hexane-EtOAc, 2:1). The solvents were removed from the filtrate and the residue was dissolved in the appropriate solvent (Et2O, THF, MeOH, or EtOH; 10 mL). Cu(OTf)2 (0.0125 mmol) was added at 0 °C and then the temperature was allowed to rise to r.t. Silica gel was added (2 g) and the solvents were removed. Purification by column chromatog-raphy gave the corresponding pure cyclopentenone derivative 8.