Conversion of α-Diazoketones into 1-Bromo-2-alkyl- or 2-arylpent-4-en-2-ols using Tin-Mediated Allylation/Propargylation

Abstract

High-yielding and mild conditions are used to prepare of 1-bromo-2-alkyl- or 2-arylpent-4-en-2-ols/1-bromo-2-alkyl- or 2-arylpent-4-yn-2-ols from α-diazoketones. The reaction involves allylation/propargylation with successive bromide insertion using in situ generated allyltin bromide/or propargyltin bromide from activated tin metal and allyl/or propargyl bromide.

Key words

tin metal - allylation - propargylation - α-diazoketones - 1-bromo-2-alkyl-ol - 2-arylpent-4-en-2-ol

• References and Notes

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• 9 General procedure: (-Diazoketone (1.00 mmol) and allyl bromide/propargyl bromide (1.50 mmol) were dissolved in THF (6.0 mL) at room temperature, then freshly activated tin metal⁵ (1.20 mmol) was added (Table 1) and the reaction was monitored by TLC. Aqueous saturated ammonium chloride (10.0 mL) was used to quench the reaction, and extraction was performed with ethyl acetate (2 × 10 mL). The combined organic extracts were dried over anhydrous Na₂SO₄ and concentrated in vacuo. Purification of the crude product by silica gel column chromatography (Merck, 100–200 mesh) using ethyl acetate and hexanes as eluent gave the desired product. ¹H and ¹³C NMR spectra and other analytical data of compounds 3a–i have been reported previously.^6,7