Mechanochemical one-pot Barbier/Simmons-Smith reaction via sequential zinc activation

Area of Science:

• Organic Chemistry
• Mechanochemistry
• Organometallic Chemistry

Background:

• Tandem reactions offer synthetic efficiency but often require careful control of reactive intermediates.
• Organozinc reagents are versatile in C-C bond formation, commonly used in Barbier and Simmons-Smith reactions.
• Mechanochemical approaches, particularly ball-milling, are emerging as sustainable alternatives to solution-phase synthesis.

Purpose of the Study:

• To develop a mechanochemical one-pot protocol for sequential Barbier and Simmons-Smith reactions.
• To utilize ball-milling for activating zinc(0) and generating organozinc intermediates in situ.
• To demonstrate the efficiency and scope of this tandem mechanochemical process for C-C bond construction.

Main Methods:

• Ball-milling was employed to activate zinc(0) for in situ generation of organozinc intermediates.
• A one-pot, sequential Barbier (allylation) and Simmons-Smith (cyclopropanation) reaction sequence was performed without intermediate work-up.
• The protocol was tested with various ketones and physical forms of zinc metal, and scaled to gram quantities.

Main Results:

• The mechanochemical protocol successfully achieved sequential allylation and cyclopropanation in a single operation.
• The reaction demonstrated broad substrate scope, tolerating a wide range of ketones and showing selectivity over other carbonyl groups.
• Enhanced diastereoselectivity was observed under minimal-solvent milling conditions in certain cases.
• The method proved compatible with different forms of zinc metal and was scalable using standard ball-milling equipment.

Conclusions:

• Mechanochemical activation of zinc(0) via ball-milling enables an operationally simple, one-pot tandem Barbier/Simmons-Smith reaction.
• This approach offers advantages over conventional solution-phase methods, particularly in simplifying tandem organometallic processes for C-C bond formation.
• Mechanochemistry provides a unique platform for developing efficient and sustainable synthetic methodologies.