Stereoselective Synthesis of 1,3-Dienes from Propargylic Alcohols by LiAlH₄/AlCl₃

Abstract

Herein we report that LiAlH₄/AlCl₃ is a very efficient reagent for the reductive dehydration of aryl propargylic alcohols in tetrahydrofuran solvent at reflux to give 1,3-dienes with good yields and high E selection. The reaction conditions are mild and easy to operate, and a variety of aryl functional groups, such as bromo, fluoro, butyl, and methoxyl groups, are tolerated. With our protocol, useful (E,E)-1,3-dienes can be synthesized.

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GRAPHICAL ABSTRACT

Keywords:

• Dehydration
• 1,3-diene
• propargylic alcohol
• reduction
• stereoselection

ACKNOWLEDGMENT

We thank the Zhejiang Scienece Foundation (No. Y4100558) for financial support.

Notes

^a The reactions were performed with 1a (1 mmol), AlCl₃ (0–3 mmol), and LiAlH₄ (0–4 mmol) in solvent (2 mL) at 70 °C for 5 h.

^b Isolated yields. The ratios of 2a, 3a, and 4a were determined by GC.

^a The reactions were performed with 1.0 mmol of 1a, 2 mmol of AlCl₃, and 3 mmol of LiAlH₄ in 2 mL of THF at 70 °C for 5 h.

^b Isolated yields.

^c The reactions were performed with 1.0 mmol of 1a and 3 mmol of LiAlH₄ in 2 mL of THF at 70 °C for 5 h and then with AlCl₃ (2 mmol) at 70 °C for 3 h.

^d The ratio of 2n1 and 2n2 was determined by ¹H NMR.