Transannular cyclization of (4S,5S)-germacrone-4,5-epoxide under basic conditions to yield eudesmane-type...

Area of Science:

• Natural Product Chemistry
• Organic Synthesis
• Sesquiterpenoid Chemistry

Background:

• Germacrone-4,5-epoxide cyclizations under acidic and thermal conditions were previously investigated.
• The reactivity of germacrone-4,5-epoxide under basic conditions remained unexplored.

Purpose of the Study:

• To investigate the chemical transformations of (4S,5S)-germacrone-4,5-epoxide under basic conditions.
• To isolate and characterize the resulting products, focusing on novel derivatives.

Main Methods:

• Treatment of (4S,5S)-germacrone-4,5-epoxide with basic reagents.
• Isolation and purification of reaction products using chromatographic techniques.
• Structure elucidation of new compounds via high-resolution mass spectrometry (HR-MS), 1D-NMR, 2D-NMR, and circular dichroism (CD) spectroscopy.

Main Results:

• Four products (compounds 2-5) were obtained from the basic treatment of germacrone-4,5-epoxide.
• Compound 2 is an isomer of the starting epoxide.
• Compounds 3-5 are eudesmane-type derivatives, with compounds 4 and 5 being novel.
• Products 3-5 possess the eudesmane carbon skeleton but exhibit distinct isoprene unit arrangements compared to natural eudesmanes.

Conclusions:

• Basic conditions induce unique rearrangements in germacrone-4,5-epoxide, leading to novel eudesmane-type sesquiterpenes.
• The study expands the known chemistry of germacrone epoxides and provides new insights into sesquiterpenoid structural diversity.