Double bonds heteroatom-carbon

Perhaps the largest class of nonaromatic unsaturated systems is that of the carbon-heteroatom double bonds, including as it does the carbonyl compounds. 

Abstract The use of A-heterocyclic carbene (NHC) complexes as homogeneous catalysts in addition reactions across carbon-carbon double and triple bonds and carbon-heteroatom double bonds is described. The discussion is focused on the description of the catalytic systems, their current mechanistic understanding and occasionally the relevant organometallic chemistry. The reaction types covered include hydrogenation, transfer hydrogenation, hydrosilylation, hydroboration and diboration, hydroamination, hydrothiolation, hydration, hydroarylation, allylic substitution, addition, chloroesterification and chloroacylation. 

The only successful [2 + 2] cycloaddition reported so far involving an MCP derivative and a carbon-heteroatom double bond is the reaction of BCP (3) with chlorosulfonylisocyanate (CSI) (594) [13b, 143], CSI is a typical [2 + 2] cycloaddend with most alkenes, but has been demonstrated to be also involved in stepwise cycloadditions via polar intermediates [157], The reaction of BCP and CSI gives the [2 + 2] cycloadduct 596 only as a minor product, besides the major [3 + 2] adduct 599 (Scheme 83) [13b, 143], Therefore, it has been reasonably suggested that both products derive from a common dipolar intermediate 595, formed by nucleophilic attack of BCP on the electron-deficient carbon of CSI (Scheme 83) [13b]. 

Scheme 4.1. Addition of CO, HCN, and RNC to carbon-carbon and carbon-heteroatom double bonds.

Cycloadditions with Carbon-Heteroatom Double Bonds. 

CYCLOADDITIONS WITH CARBON-HETEROATOM DOUBLE BONDS... 

Photochemical or thermal extrusion of molecular nitrogen from ot-diazocarbonyl compounds generates a-carbonylcarbenes. These transient species possess a resonance contribution from a 1,3-dipolar (303, Scheme 8.74) or 1,3-diradical form, depending on their spin state. The three-atom moiety has been trapped in a [3 + 2] cycloaddition fashion, but this reaction is rare because of the predominance of a fast rearrangement of the ketocarbene into a ketene intermediate. There are a steadily increasing number of transition metal catalyzed reactions of diazocarbonyl compounds with carbon-carbon and carbon-heteroatom double bonds, that, instead of affording three-membered rings, furnish hve-membered heterocycles which... 

Cycloadditions with Carbon-Heteroatom Double Bonds. 557... 

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