Allylmagnesium Halides Do Not React Chemoselectively Because Reaction Rates Approach the Diffusion Limit
Jacquelyne A Read1, K A Woerpel1
1Department of Chemistry, New York University , 100 Washington Square East, New York, New York 10003, United States.
Allylmagnesium halides rapidly add to carbonyl compounds, reacting at near-diffusion rates. Unlike other organometallic reagents, they show little selectivity between different carbonyl substrates, even esters and aldehydes.
Area of Science:
- Organic Chemistry
- Organometallic Chemistry
Background:
- Organomagnesium reagents are widely used in organic synthesis for carbon-carbon bond formation.
- Reactivity and selectivity of organometallic additions to carbonyl compounds are crucial for synthetic efficiency.
Purpose of the Study:
- To investigate the reactivity of allylmagnesium halides in additions to various carbonyl compounds.
- To compare the reactivity profile of allylmagnesium halides with other organomagnesium and organolithium reagents.
Main Methods:
- Competition experiments were conducted to compare reaction rates.
- A range of carbonyl compounds, including aldehydes, ketones, and esters, were used as substrates.
- Reactions were monitored to determine relative rates of addition.
Main Results:
- Allylmagnesium halides reacted with most carbonyl compounds at rates approaching the diffusion limit.
- Unlike alkylmagnesium and alkyllithium reagents, allylmagnesium halides showed minimal differentiation between electronically or sterically diverse carbonyl substrates.
- Additions to esters occurred at rates competitive with aldehydes, and only highly hindered substrates showed significantly slower reaction rates.
Conclusions:
- Allylmagnesium halides exhibit exceptionally high and non-selective reactivity towards carbonyl compounds.
- This unique reactivity profile suggests potential applications where rapid, unselective carbon-carbon bond formation is desired.
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