Electrophilic acylation

Both the Reimer-Tiemann and the Vilsmeier reactions lead to formylation in the 5-position in pyrimidines with at least two strongly releasing substituents <1994HC(52)1>. The reaction of metallated intermediates with acyl electrophiles can be used to give acyl derivatives <2001T4489>, and direct carbamoylation of 6-aminouracil derivatives 87 has been achieved under microwave-assisted conditions to give 88 <2005S2713>. 

The acyl halides (RCOX) on treatment with anhydrous aluminium chloride (AICI3) give a complex, which decomposes to give acyl electrophile, an acylium ion (RCO+). Friedel-Crafts acylation of aromatic compounds involves the formation of a carbocation that acts as an electrophile (see section 2.1.3). 

Other reports of (jj -allyl)Fe(CO)3R complexes are much more scattered and much less systematic. At least three general types of reactions have been observed in more than one case. First, the reaction of (diene)Fe(CO)3 complexes with electrophilic alkenes gives aUyhron complexes in two different ways. If the diene in question is acylic, electrophilic attack at C-1 of the diene gives compounds of type (158) (equation 33). In the case of substituted rj -cycloheptatriene-or azepine-Fe(CO)3 complexes, reaction... 

Entry Alkynylmetal Aryl, Alkenyl, or Acyl Electrophile" Pd Catalyst Product Yield (%) Reference... 

There are six discrete combinations for Pd-catalyzed cross-coupling between homoallyl-, homopropargyl-, or homobenzyhnetals and alkenyl or aryl electrophiles (Scheme 4). In addition to these processes, those involving alkyl, allyl, benzyl, propargyl, alkynyl, and acyl electrophiles are conceivable, and some have indeed been observed. However, these reactions are discussed in other pertinent sections. 

This section mainly deals with Pd-catalyzed reactions of aryl, alkenyl, benzyl, alkyl, and acyl electrophiles with metal nucleophiles M = Si, Ge, Sn, B, and transition metals) leading to carbon-metal bond formation (Scheme 1). Allylic and related metallations are described in Sect. V.2.3.3, The reaction mechanism is generally believed to involve, firstly, oxidative addition of R—X to a Pd(0) species second, transmetallation of the resulting Pd(II) species with M—M and finally, reductive elimination forming R—M and the active Pd(0) species. However, another catalytic cycle via oxidative addition of M—M to Pd(0) species is also proposed. ... 

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