Carbenoid: Difference between revisions

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In chemistry a carbenoid is a reactive intermediate that shares reaction characteristics with a carbene.^[1] In the Simmons–Smith reaction the carbenoid intermediate is a zinc / iodine complex that takes the form of

I-CH₂-Zn-I

This complex reacts with an alkene to form a cyclopropane just as a carbene would do.

Carbenoids appear as intermediates in many other reactions. In one system a carbenoid chloroalkyllithium reagent is prepared in situ from a sulfoxide and t-BuLi which reacts the boronic ester to give an ate complex. The ate complex undergoes a 1,2-metallate rearrangement to give the homologated product, which is then further oxidised to a secondary alcohol.^[2]

The enantiopurity of the chiral sulfoxide is preserved in the ultimate product after oxidation of the boronic ester to the alcohol indicating that a true carbene was never involved in the sequence.

References

^ Organic Chemistry john McMurry Brooks /Cole Publishing Company 1988 ISBN 0-534-07968-7
^ Iterative Stereospecific Reagent-Controlled Homologation of Pinacol Boronates by Enantioenriched -Chloroalkyllithium Reagents Paul R. Blakemore and Matthew S. Burge J. Am. Chem. Soc.; 2007; 129(11) pp 3068 - 3069; (Communication) doi:10.1021/ja068808s

[1] Organic Chemistry john McMurry Brooks /Cole Publishing Company 1988 ISBN 0-534-07968-7

[2] Iterative Stereospecific Reagent-Controlled Homologation of Pinacol Boronates by Enantioenriched -Chloroalkyllithium Reagents Paul R. Blakemore and Matthew S. Burge J. Am. Chem. Soc.; 2007; 129(11) pp 3068 - 3069; (Communication) doi:10.1021/ja068808s

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 This complex reacts with an [[alkene]] to form a [[cyclopropane]] just as a carbene would do.
-Carbenoids appear as intermediates in many other reactions. In one system a carbenoid chloroalkyllithium reagent is prepared in situ from a [[sulfoxide]] and [[organolithium|t-BuLi]] which reacts the boronic ester to give an ate complex. The ate complex undergoes a 1,2-metallate rearrangement to give the homologated product, which is then further oxidised to a secondary alcohol.<ref>Iterative Stereospecific Reagent-Controlled Homologation of Pinacol Boronates by Enantioenriched -Chloroalkyllithium Reagents [[Paul R. Blakemore]] and Matthew S. Burge [[J. Am. Chem. Soc.]]; '''2007'''; 129(11) pp 3068 - 3069; (Communication) {{DOI|10.1021/ja068808s}}</ref>
+Carbenoids appear as intermediates in many other reactions. In one system a carbenoid chloroalkyllithium reagent is prepared in situ from a [[sulfoxide]] and [[Tert-Butyllithium|t-BuLi]] which reacts the boronic ester to give an ate complex. The ate complex undergoes a 1,2-metallate rearrangement to give the homologated product, which is then further oxidised to a secondary alcohol.<ref>Iterative Stereospecific Reagent-Controlled Homologation of Pinacol Boronates by Enantioenriched -Chloroalkyllithium Reagents Paul R. Blakemore and Matthew S. Burge [[J. Am. Chem. Soc.]]; '''2007'''; 129(11) pp 3068 - 3069; (Communication) {{doi|10.1021/ja068808s}}</ref>
 :[[Image:CarbenoidApplication.png|500px|Insertion of carbenoid into C-B bond]]
-The [[enantiopurity]] of the chiral sulfoxide is preserved in the ultimate product after oxidation of the boronic ester to the [[alcohol]] indicating that a true carbene was never involved in the sequence.
+The [[enantiopurity]] of the chiral sulfoxide is preserved in the ultimate product after oxidation of the boronic ester to the [[Alcohol (chemistry)|alcohol]] indicating that a true carbene was never involved in the sequence.
 ==See also==