Lecture 14 - Nitrenes and Carbenes

One lone pair is in an sp hybrid while the other

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Unformatted text preview: and the metallocarbenoid complex. Intermolecular C- H inser?on: the use of donor/acceptor diazo- compounds and the advent of new catalysts has promoted important development in increasing the selec5vity. Regioselec5vity: below is a study in the selec5vity of various substrates in the C- H inser5on with phenyl- diazoacetate and Rh2(S- DOSP)4 cat. (Davies Chem. Rev. 2003, 103, 2861) F. Sladojevich Reactivity: Rearrangements and Ylide formations Rearrangements: Rearrangement is another common reac5on of carbenes as exemplified by the following reac5ons: Chem 106 Ylide formaKon: Carbenes can func5on as Lewis acids by interac5ng with a pair of nonbonding electrons contributed by a Lewis base. If the Lewis base is an uncharged species, ylides are generated. (Padwa, Chem. Rev. 1991, 263; Chem. Rev. 1996, 223). Generally, the carbene precursor is a diazoalkane or, more frequently, a diazocarbonyl reagent. These can be decomposed via thermolysis or photolysis. However, the most common method involves cataly5c transi5on metals, such as Cu or Rh. X is onen S, O, or N and can be sp2 or sp3 hybridized. Subsequently, ylides onen undergo sigmatropic rearrangements or cycloaddi5ons. F. Sladojevich Vinylidenes Chem 106 q༇  Vinylidenes Similar to carbenes, vinylidene carbenes are accessible by alpha- elimina5on. These species undergo similar reac5ons as observed for carbenes, i.e. cyclopronana5on, rearrangements, or C- H- inser5ons. Recall these classic reac5ons: F. Sladojevich Reactivity:...
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This document was uploaded on 02/27/2014 for the course CHEM 106 at Harvard.

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