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Phospha-Michael additions to activated internal alkenes: steric and electronic effects
Heather K Lenker1, Marcia E Richard, Kyle P Reese
1Department of Chemistry, Bucknell University, Lewisburg, Pennsylvania 17837, USA.
The Journal of Organic Chemistry
|January 17, 2012
Summary
This study demonstrates a novel, catalyst-free method for adding P(O)-H bonds to internal alkenes. This phospha-Michael reaction proceeds efficiently under solvent-free conditions, offering a greener synthetic route.
Area of Science:
- Organic Chemistry
- Organophosphorus Chemistry
Background:
- The addition of phosphorus-containing functional groups to unsaturated organic molecules is crucial for synthesizing various organophosphorus compounds.
- Developing efficient and environmentally friendly synthetic methodologies for these transformations remains an active area of research.
Purpose of the Study:
- To report a novel, catalyst- and initiator-free method for the addition of P(O)-H bonds to internal alkenes.
- To explore the scope and limitations of this reaction using various activated and less activated alkene substrates.
Main Methods:
- The reaction involves the direct addition of a secondary phosphine oxide to internal alkenes under solvent-free conditions.
- Substrates included cinnamates, crotonates, coumarins, sulfones, chalcones, isopropylidenemalononitrile, and ethyl 2-cyano-3-methyl-2-butenoate.
- Reaction conditions ranged from room temperature trituration to microwave heating (>150 °C) for less activated substrates.
Main Results:
- Successful functionalization of a range of internal alkenes with P(O)-H bonds was achieved.
- Highly activated alkenes reacted readily at room temperature.
- Less activated alkenes required elevated temperatures, with microwave irradiation proving effective.
- A competing disproportionation reaction of the phosphine oxide was observed at high temperatures for less activated substrates.
Conclusions:
- A new, efficient, and green method for the phospha-Michael reaction of secondary phosphine oxides with internal alkenes has been developed.
- The reaction offers a valuable tool for organophosphorus synthesis, proceeding without catalysts or initiators.
- Understanding substrate activation and potential side reactions is key for optimizing the process.
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