α-Diketones as acyl anion equivalents: a non-enzymatic thiamine-promoted route to aldehyde-ketone coupling in PEG400 as recyclable medium

By mimicking the peculiar behavior of thiamine diphosphate-dependent acetylacetoin synthase, it has been demonstrated that thiamine hydrochloride 2a and its simple analogue thiazolium salt 2b are able to activate α-diketones as acyl anion equivalents in nucleophilic acylations, such as the homo-coupling of α-diketones and the hitherto unreported cross-coupling between α-diketones and α-ketoesters. These carboligation reactions were optimized under stoichiometric (2a) and catalytic conditions (2b) by using eco-friendly PEG₄₀₀ as the reaction medium, thus allowing both solvent and thiazolium salt recycling.     

Synthesis of fluorinated α-diketones and some intermediates

Reactions of perfluoroalkylcopper compounds with α-ketoacyl chlorides were used for the synthesis of fluorinated α-diketones. Heptafluoropropylcopper prepared from copper bronze and 1-iodoheptafluoropropane reacted with benzoylformyl chloride to give heptafluoro-1-phenyl-1,2-pentanedione, with trimethylpyruvyl chloride to give 2,2-dimethyl-5,5,6,6,7,7,7-heptafluoro-3,4-heptanedione, and with 3,3,4,4,5,5,5-heptafluoro-2-ketopentanoyl chloride or oxalyl chloride to give tetradecafluoro-4,5-octanedione. Syntheses of fluorinated acetylenes, cyanohydrins, α-hydroxy acids, α-keto acids, their chlorides, and other intermediates for the syntheses of α-diketones by the above route and by other methods are described. An interesting seven-membered ring containing β-hydroxy ketone was obtained by an intramolecular aldol condensation of a fluorinated bis(methyl) ketone.     

Stereocontrolled acylation of (η4-cycloheptatriene)iron tricarbonyl

The anion derived by deprotonating (cycloheptatriene)Fe(CO)₃ reacts with acid chlorides to give exo C-7 substitution. The acyl group is readily isomerized to C-5 on treatment with base. The C-7 acylated products can be deprotonated; the resulting anions react at oxygen with acyl chlorides and Me₃SiCl, and at carbon with MeI.     

A versatile access to unsymmetrical and symmetrical α-diketones via organotin reagents

Unsymmetrical α -diketones have been obtained via cross coupling of acyltins with acyl halides under PdCl₂(PPh₃)₂ catalysis while symmetrical α -diketones have been readily obtained via “in situ” formation of acyltins using hexabutylditin and acyl chlorides under similar experimental conditions.     

Thiazolium-catalyzed intermolecular Stetter reaction of linear and cyclic alkyl α-diketones

An efficient method for the N-heterocyclic carbene (NHC)-catalyzed conjugate addition of acetyl anions to various α,β-unsaturated acceptors (Stetter reaction) has been optimized by using 2,3-butandione (biacetyl) as an alternative surrogate of acetaldehyde. The disclosed procedure proved to be compatible with microwave dielectric heating for reaction time reduction and with the use of different linear α-diketones as acyl anion donors (e.g. 3,4-hexanedione for propionyl anion additions). Moreover, the unprecedented umpolung reactivity of cyclic α-diketones in the atom economic nucleophilic acylation of chalcones is herein presented. Mechanistic aspects of the thiazolium-based catalysis involving linear and cyclic α-diketone substrates are also discussed.     

Coupling of imidoyl chlorides to diazadienes by anionic nickel complexes

Imidoyl chlorides react with aroyltricarbonylnickelates, under mild conditions, to give 1,4-diaza-1,3-butadienes and α-diketones. An electron transfer mechanism is proposed for this reaction.     

A Facile Route to Convert Acetylacetone into Other β-Diketones with Acyl Chlorides Promoted by Samarium Triiodide

Reaction of acetylacetone with acyl chlorides in the presence of SmI₃ gave β-diketones RCOCH₂COCH₃ (I) or RCOCH₂COR (II) in good yields under mild and neutral conditions.     

Proline-catalyzed aldol reactions of acyl cyanides with acetone: an efficient and convenient synthesis of 1,3-diketones

The aldol-type addition of acetone towards (un)substituted benzoyl, heteroarylcarbonyl or α,β-unsaturated acyl cyanides was efficiently catalyzed by l-proline (30 mol %) to give 2-hydroxy-4-oxo-2-substituted pentanenitriles. Upon the treatment with sodium hydroxide, the adducts transformed to 1,3-diketones in good-to-excellent yield, furnishing an efficient and convenient method for the regioselective synthesis of 1,3-diketones.     

β-Diketone Synthesis by Reaction of α-Haloketones with Acid Chlorides or Acid Anhydrides Promoted by Samarium Triiodide

Promoted by SmI₃, α-haloketones were reacted with acid chlorides or acid anhydrides and β-diketones were synthesized via intermediate samarium enolates.     

Rhenium complex-catalyzed acylative cleavage of ethers with acyl chlorides

It was found that rhenium complex was an efficient catalyst for the acylative cleavage of C-O bond of ethers with acyl chlorides. When acyclic ethers were allowed to react with acyl chlorides in the presence of a catalytic amount of ReBr(CO)₅, acylative cleavage of C-O bond of acyclic ethers smoothly proceeded to give the corresponding esters in moderate to good yields. Similarly, cyclic ethers were acylative cleaved by acyl chlorides to give the corresponding chloro substituted esters in good yields by the use of Re₂O₇ catalyst.     

Herstellung von 1, 3-Diketonen und von Nitro-diketonen durch (1:1)-Acylierungen von Lithiumenolaten mit Acylchloriden

Preparation of 1,3-Diketones and of Nitro-diketones by (1:1)-Acylation of Lithium Enolates with Acyl Chlorides Slow addition of precooled solutions of lithium enolates in THF (Fig. 1) to solutions of equimolar amounts of acyl chlorides in the same solvent at temperatures between ? 80 and ? 100° furnishes 1, 3-diketones in acceptable to good yields (Tables 1?3). Even 3-nitropropionyl and 4-nitrobutyryl chloride can be employed for the (1:1)-acylation of enolates to give the synthetically useful 5- and 6-nitro-1, 3-diketones 13 and 25 , respectively. The scope and the limitations of this method of preparing 1, 3-diketones are given and are compared with alternative methods.     

Synthesis and desilylation of some bis(trimethylsilyl)alkenes and polymers bearing bis(silyl)alkenyl groups

The synthesis of various vinylbis(silanes) from some aryl and heteroaryl aldehydes and (Me₃Si)₃CLi in Et₂O is described. Friedel-Crafts reaction of 1,1-bis(trimethylsilyl)-2-(2-naphthyl)ethene with various acyl chlorides (RCOCl, R = Me, Et, i-Pr, i-Bu, n-pent) gave the corresponding α-silyl-α,β-unsaturated enones with high E steroselectivity. Moreover, poly(styrene)-co-[2,2-bis(trimethylsilyl)ethenyl(styrene)] obtained via the reaction of polymers bearing pendant enone functions and (Me₃Si)₃CLi, reacts with the same acyl chlorides in the presence of catalytic amount of AlCl₃ to give the new macromolecules bearing α-silyl-α,β-unsaturated enones and α,β-unsaturated enones.     

Reactions of enamines with fluorinated acyl chlorides----Synthesis of fluorinated 1,3-diketones and 1,3-keto-aldehydes

The reactions of enamines (1a-b,4,6) with fluorinated acyl chlorides (2a-d) produced fluorinated 1,3-diketones (3a-f) and 1,3-keto-aldehydes (7a-c) in good yields as well as byproducts fluorinated acylamides (5a-c).It is proposed that the reactions involve nucleophilic attack by the C-atora and/or N-atom of the enamines on acyl carbon of the fluorinated acyl chlorides.     

Reductive Cleavage of the S-Si Bond in Phenylthio-trimethylsilane:A Novel Method for the Synthesis of Thiolesters

TheaPPlicationofsamariumdiiodideinorganicSyntilesishasreceivedmoreandmoreattenhoninthelastdecade.'-'Itisapowerfulone-electrontr~ferreducest.Recently,wehaveconsideredthattheS-Stbondmightbereductivelycleavedwithsamariumdiiodide.Thiolestersareusefulintermediatesinorgbocchemistry.'-'Manynewmethodshavebeendevelopedforthepreparationoftlilolestersinrecentyears,'-"forexample,tilereachonbetWeensodiumthiobenzoateandarenediazoniumtetaluoroborates,'beatmentofnitrosoamidesornitroamideswithinercaptansint…     

Reactions of organometallic compounds catalyzed by transition-metal complexes: XI. The palladium-catalyzed reaction of acyl chlorides with Et6Sn2 as a route to symmetrical ketones and α-diketones

The reaction of aroyl chlorides (ArCOCl) with Et₆Sn₂ gives symmetrical ketones (Ar₂CO) or α-diketones ((ArCO)₂), depending on the nature of the palladium catalyst and the reaction conditions. The synthesis of α-diketones from AlkCOCl and HetCOCl has been performed for Alk = n-C₇H₁₅ and Het = 2-C₄H₃O (furyl). The palladium-catalyzed carbonylation of aryl iodides in the presence of Et₆Sn₂ may serve as another route to symmetrical α-diketones. Such a possibility has been demonstrated for the preparation of 4,4′-dimethoxybenzil from 4-iodoanisole, carbon monoxide, and Et₆Sn₂.     

Reductive Cleavage of S-S Bond in Diphenyl Disulfide by Samarium Diiodide: A Novel Method for the Synthesis of Thiolesters

Diphenyl disulfide is reduced by samarium diiodide to yield samarium phenylthiolate. This new thiolate anion species mildly reacts with acyl chlorides to give thiolesters in good yields.     

Novel Bifunctionalization of Activated Methylene: Base-Promoted Trifluoromethylthiolation of β-Diketones with Trifluoromethanesulfinyl Chloride

A novel bifunctionalization of activated methylene was achieved successfully through the base-promoted trifluoromethylthiolation of β-diketones or β-ketoesters with trifluoromethanesulfinyl chloride. A series of α-trifluoromethylthiolated α-chloro-β-diketones and α-chloro-β-ketoesters were obtained in moderate to good yields under mild conditions. When β-diketones containing a phenyl group with a hydroxyl or amino substituent at the ortho position were used as substrates, intramolecular trifluoromethylthiolation/cyclization reaction took place to give the corresponding cyclic products. Furthermore, the protocol could be extended to perfluoroalkylthiolation with the sodium perfluoroalkanesulfinate/POCl₃ system. On the basis of experimental results, plausible mechanisms are proposed.     

Direct Umpolung Morita–Baylis–Hillman like α-Functionalization of Enones via Enolonium Species

Herein we report on the umpolung of Morita–Baylis–Hillman type intermediates and application to the α-functionalization of enone C−H bonds. This reaction gives direct access to α-chloro-enones, 1,2-diketones and α-tosyloxy-enones. The latter are important intermediates for cross-coupling reaction and, to the best of our knowledge, cannot be made in a single step from enones in any other way. The proposed mechanism is supported by spectroscopic studies. The key initial step involves conjugate attack of an amine (DABCO or pyridine), likely assisted by hypervalent iodine acting as a Lewis acid leading to formation of an electrophilic β-ammonium-enolonium species. Nucleophilic attack by acetate, tosylate, or chloride anion is followed by base induced elimination of the ammonium species to give the noted products. Hydrolysis of α-acetoxy-enones lead to formation of 1,2-diketones. The α-tosyl-enones participate in Negishi coupling reactions under standard conditions.     

Synthesen von 2-Pyronen aus α, β-ungesättigten Säurechloriden und tertiären Aminen

A new synthesis of 2-pyrones has been developed. Two molecules of α, β-unsaturated acid chlorides ( 8 , 12 and 18 ) condense, with loss of two molecules hydrogen chloride, to pairs of substituted 2-pyrones ( 9 and 10 , 13 and 14 , 19 and 20 ) when treated with triethyl amine in chloroform or methylene chloride at room temperature. In the case of 18 , two additional products were obtained, namely the resorcinol derivative 21 and traces of the 1, 3-cyclobutanedione derivative 22 . Under the same conditions the α, β-unsaturated acid chlorides 8 , 15 , 18 and 41 were condensed with trichloroacetyl chloride to give 6-trichloromethyl-2-pyrones ( 42 , 43 , 44 and 46 ). These 2-pyrones are valuable intermediates for the synthesis of 6-carboxy-2-pyrones and 6-methyl-2-pyrones. A methyl group in β-position of the α, β-unsaturated acid chloride appears to be essential for the described condensations, for the acid chlorides 16 and 17 did not yield defined products and the acid chloride 40 reacted with trichloroacetyl chloride in a very low yield. It is considered that the described reactions proceed via the 1, 4-addition of an acid chloride to a vinyl ketene or through the acylation of an intermediate anion by an acyl derivative as outlined in reaction scheme 1. The structures of the 2-pyrones were confirmed by their spectroscopic properties, summarized in table 3, and by some of their chemical transformations.     

t-Butyldiphenylsilyl-Lithium and Lithium Bis(t-Butyldiphenylsilyl)Cuprate. New Silylating Reagents

t-Butyldiphenylsilyl-lithium reacts with carbonyl derivatives to give α -hydroxysilanes in high yields. Lithium bis (t-butyldiphenylsilyl)cuprate reacts with α, β-unsaturated ketones and esters and with acyl chlorides to give β-silylcarbonyl1 compounds and acylsilanes. β-t-Butyldiphenylsilylketones are masked α, β-unsaturated ketones.