Intermolecular reactions ketone trapping

Radical species derived from reduction of ketones are also trapped by alkenes in an intermolecular reaction. Reaction only occurs with terminal alkenes of the type... 

Intramolecular [80] and intermolecular [81,82] trapping of acylpalladium intermediates with enolates has been studied. Intermolecular versions can involve trapping with both C- and 0-enolates. The Pd-catalyzed carbonylation reactions of alkenyl iodides in the presence of various ketone enolate precursors displayed an interesting dichotomy the expected 0-enolate trapping product 47 may undergo cyclization to give six-membered lactone 48, and the product s composition critically depends on the amount of a base and the structure of ketones (Scheme 9.19). 

Addition of alkyl radicals to alkenes is a useful C-C bond formation reaction in which a a-C-C bond is made from a n-C-C bond in a very exothermic reaction. In contrast, n-C-O bonds of ketone and aldehyde are nearly as strong as a-C-C bonds. Therefore, ketones and aldehydes cannot be used as intermolecular traps in synthesis (Scheme 2.7). 

Under strictly anhydrous conditions, the iminophosphorane intermediate that is formed as a result of the Staudinger reaction can react with aldehydes and ketones in an intermolecular fashion (as in the synthesis of imine 36 described above) or intramolecularly with a variety of carbonyl containing functional groups to afford a host of products. Nitrogen containing ring systems such as cyclic imines (44) represent just one of the many products one can prepare and the reaction is particularly well suited for the facile synthesis of five, six, and seven-membered rings. In addition to aldehydes and ketones, carboxylic acids, esters, thio-esters, and amides can also react in an intramolecular fashion to trap an iminophosphorane to afford a variety of heterocycles. Examples from the current literature are described in Section 2.5.5. 

Since Kharasch reported radical-mediated carboxylation of saturated hydrocarbons with phosgene as a radical trap in the 1940s [39], no successful radical acylation and carboxylation reactions have appeared. In intermolecular radical acetylations, biacetyl was used as a radical trap (Scheme 18) [44]. The addition of an alkyl radical to the carbonyl carbon of biacetyl gives the methyl ketone along with an acetyl radical. 

In contrast to the diverse insertion chemistry of vinylpalladium intermediates discussed in Sects. IV.3 and IV.5, the reactions of vinylpalladium complexes with electrophiles had not been reported until recently. Although a single report on the annulation of the o-mer-curio benzaldehyde with diphenylacetylene into the corresponding indenols and inde-nones catalytic in palladium and stoichiometric in copper had been communicated in 1992, the more synthetically useful protocol for the catalytic version of this type of transformation remained unknown until 1999. In this section the intermolecular carbopalladation of alkynes with aryl halides followed by the intramolecular trapping of the formed vinylpalladium species with ketones, aldehydes, and nitriles will be discussed. 

The variations of intramolecular—intermolecular and intramolecular-intramolecular DTHDA sequences of this cross-conjugated thiatriene system have been reported (Scheme 2.4) [10], The thiatrienes 6 generated from the corresponding ketones by thionation with Lawesson s reagent in refluxing benzene were trapped in situ by the internal dienophile to give the initial HDA monoadducts 7. The second DA reaction of each separated stereoisomer 7... 

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