Acyl-dicarbonyl complexes

The achiral dicarbonyl complex 1 has been shown to undergo facile 1,4-addition of amines and thiols to generate the elaborated acyl complexes 2. The more nucleophilic sulfur atom of 2-mercaptoethanol selectively adds to such complexes45. 

On the other hand, reaction of the rhodium(I) hydrido complex RhH(CO)(PPh3)3 with styrene and with carbon monoxide at atmospheric pressure, monitored by NMR spectroscopy, showed the presence of the branched acyl dicarbonyl species given in reaction (o), followed by its isomerization to the linear isomer and formation of the aldehyde. 

The commercially available (tj5-cyclopentadienyl)iron dicarbonyl dimer 1 is the source of the carbonyl(//5-cyclopentadienyl)iron(L) moiety. Reductive or oxidative cleavage of 1 provides reactive monomeric species that may be converted into iron-acyl complexes as described in the following sections (see also Houben-Weyl, Vol. 13/9a, p208). 

An oxazole substituted with a complex aminohydantoin side chain is described as a muscle relaxant. Imine formation between glyoxylic acid and aminohydantoin (38-1) results in the imino acid (38-2). Use of that intermediate to acylate the amine on 4-chloro-2 -aminoacetophenone (38-3) leads to the amide (38-4), which now includes a 1,4-dicarbonyl array. Treatment of the keto-amide with phosphorus... 

Many other iron complexes (t -alkyls, t -acyls, t -ynyls, cationic -alkenes, and carbenes) are ultimately erived from either sodium dicarbonyl(cyclopentadienyl)... 

A second entry to dicarbonyl substrates utilizes the aldol reaction to establish the a-methyl center prior to oxidation of the p-hydroxyl moiety. Commonly, this oxidation is performed using the Sulfur Trioxide-Pyridine complex, which results in <1% epimerization of the methyl-bearing center (eq 34). Interestingly, this procedure procures the opposite methyl stereochemistry from that obtained through enolate acylation of the same enantiomer of oxazolidinone. 

In the case of -dicarbonyl substituted ylides (8, R =COR ) the situation is more complex, but in nearly all cases NMR spectra suggest that the molecules exist as Z, Z-isomers °. Exceptions may arise if the acyl group is stabilized in an alternative configuration by intramolecular hydrogen bonding . 

In reductive acylation and dimerization, the cathode is often superior to dissolving metal or radical anions reductants. So a, j6-unsaturated ketones or esters can be acylated in high yield to 1,4-dicarbonyl compounds at the mercury cathode [39], but the corresponding reaction with sodium in tetrahydrofuran (THE) fails [40]. On the other hand, reductive acylation of double bonds becomes possible in high yield, when vitamin Bj2 is used as mediator [41]. Here cobalt-alkyl complexes play a decisive role as intermediates. 

Acyl complexes of ruthenium(II), Ru(COR)Cl(CO)(PPh3)2 (R = Me, Et), were prepared" by reacting the hydrido species RuH(Cl)(CO)(PPh3)3 with acetaldehyde or propionaldehyde, respectively. The acetyl derivative slowly reacts with CO to give the dicarbonyl compound ... 

Some lactones serve as starting material. y-Phenylazo-y-valerolactone is thermally rearranged to a mixture of pyridazinones 20 and 21 in a ratio of 1.75 1. A complex mechanism is proposed. Pyridazines also result from hydrazines and substituted y-lactones - or -acyl-y-lactones, which react as 1,4-dicarbonyl compounds. y-Chloroketones react with substituted hydrazines to gives pyridazines or Af-aminopyrrolines, depending upon the hydrazine used. ° y-Chlorobutanal gives the corresponding 1,4,5,6-tetrahydropyridazine. ... 

Complementary to the acylation of enolate anions is the acid-catalyzed acylation of the corresponding enols, where the regiochemistry of acylation can vary from that observed in base-catalyzed reactions. Although the reaction has been studied extensively in simple systems, it has not been widely used in the synthesis of complex molecules. The catalysts most frequently employed are boron trifluoride, aluminum chloride and some proton acids, and acid anhydrides are the most frequently used acylating agents. Reaction is thought to involve electrophilic attack on the enol of the ketone by a Lewis acid complex of the anhydride (Scheme 58). In the presence of a proton acid, the enol ester is probably the reactive nucleophile. In either case, the first formed 1,3-dicarbonyl compound is converted into its borofluoride complex, which may be decomposed to give the 3-d>ketone, sometimes isolated as its copper complex. 

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