A, 3-Ynones

Several other versions of these catalysts have been developed. Arene complexes of monotosyl-l,2-diphenylethylenediamine ruthenium chloride give good results with a,(3-ynones.55 The active catalysts are generated by KOH. These catalysts also function by hydrogen transfer, with isopropanol serving as the hydrogen source. Entries 6 to 8 in Scheme 5.3 are examples. 

Intramolecular Michael addition.1 Cesium carbonate catalyzes the intramolecular Michael addition of a cyclic (3-keto ester to an a,(3-ynone to form a cyclic enone after protonation. This reaction proceeds readily when a five- or six-mem-bered ring is formed higher rings can be formed, but in low yield.1... 

Enantioselective Reduction ofa,P-Ynones. Oxazaborolidine ligands 1 are among the most effective catalysts for the enantioselective reduction of ketones to secondary alcohols. Substitution of the methyl or butyl group on boron by a trimethylsilylmethyl group led to a much improved catalyst for the catecholborane mediated reduction of a, 3-ynones. For example, the enantioselectiv-ities for the reduction of an a, 3-ynone was improved from 60% to 98.5% when the nature of the R group was modified (eq 1). ... 

These pentahydrides have attracted attention as catalysts for hydrogenation of the double bond in alkenes. IrH5(PPr3)2 catalyses vinylic H-D exchange between terminal alkenes and benzene, the isomerization of a,(3-ynones, isomerization of unsaturated alcohols and dehydrogenation of molecules such as secondary alcohols [176]. 

A study of the conversion of amino acids to chiral a-amino -a,3-ynones (25) has been published and the reaction of N-alkylcarbamate-protected amino-acid isoxazolidides with aIkynyl-lithiums proved to be the method of choice. An alternative, boron-based, method for the preparation of ynones is summarised in Scheme 12. Although the yields were somewhat... 

The ease with which the dipolarophile interacts with vinylacetylenes depends mainly on a spatial factor. The study of the reactions of alkylthiobuten-3-ynones-l and their selenic and telluric analogs with DPNT shows that, in this case, nitrilimine also acts as a nucleophilic agent with a nucleophilic center on the carbon atom of the 1,3-dipole and always adds to the terminal carbon of the enyne system to form l,3-diphenyl-5-/ -2-pyrazolenines. The oxidation of the latter with chloranil leads to alkynylpyrazoles (65ZOR51). 

Aniinophenyl)-a,(J>-ynones react with nitrile oxides by domino [3 + 2] cycloaddition/annulation reactions, giving rise to isoxazolo[4,5-c]quinolines in satisfactory yields (434). Nitrile oxides undergo addition to allylzinc bromide to generate 5-butenylisoxazolines in good yields. The domino reaction combines 1,3-cycloaddition with Wurtz coupling (435). 

Carbon monoxide rapidly inserts into the carbon—zirconium bond of alkyl- and alkenyl-zirconocene chlorides at low temperature with retention of configuration at carbon to give acylzirconocene chlorides 17 (Scheme 3.5). Acylzirconocene chlorides have found utility in synthesis, as described elsewhere in this volume [17]. Lewis acid catalyzed additions to enones, aldehydes, and imines, yielding a-keto allylic alcohols, a-hydroxy ketones, and a-amino ketones, respectively [18], and palladium-catalyzed addition to alkyl/aryl halides and a,[5-ynones [19] are examples. The acyl complex 18 formed by the insertion of carbon monoxide into dialkyl, alkylaryl, or diaryl zirconocenes may rearrange to a r 2-ketone complex 19 either thermally (particularly when R1 = R2 = Ph) or on addition of a Lewis acid [5,20,21]. The rearrangement proceeds through the less stable... 

Reduction of a,p-ynones. a,/J-Acetylenic ketones are reduced by 1 to (S> propargyl alcohols in 86-96% enantioselective purity. It is thus comparable to B-3-pinanyl-9-BBN in enantiomeric yields, although the reductions require 1-2 days and an excess of neat reagent for complete reaction. 

Hydrogenation of an a,P-ynone, 3-decyn-2-one (14), to the corresponding cA-enone was successful withPd-CaC03 as catalyst (eq. 4.17).52 It was necessary to use a rather... 

Acylzirconocene chloride complexes behave as an acyl group donor toward unsaturated a,/3-enones and -ynones under Pd-Me2Zn(Me2AlCl)-catalyzed conditions to give stereoselectively bicyclo[3.3.0] compounds (Equation 92) <20020L4061>. A mechanistic rationale for the reaction sequence has been given. 

Syntheses of 1,5-benzothiazepines can be achieved through various routes starting from 2-aminothiophenol and 1,3-drfunctional three-carbon budding blocks [184, 185]. Among them, a,(3-unsaturated carbonyl compounds such as enones [186-188] and ynones [189-192] are suited best for Michael addition and subsequent cyclocondensation. 

Hydroboration of the C-C unsaturated bond may be a possible side reaction in the reduction of a,P-unsatuxated ketones. However, in many cases, some ox-azaborolidines successfully catalyze the selective reduction of ketone carbonyls (Scheme 6). The borane reduction of 2-methylnon-l-en-3-one with oxazaborolidine 45 showed a clean conversion to the allylic alcohol (98%, 92% ee S) [82]. The same catalyst [83] and 4b [84] were effective for the reduction of a,P-ynones [83]. 

P-carbohnes [29] (Schane 3, equation 1). A variety of secondary amines were employed, and the method was adapted to the preparation of pyrrolo[3,2-/lindoles and dipyrrolo[3,2-h 2, 3 -c]pyridines [30]. Cacchi and colleagues synthesized 3-aroylindoles from the copper-catalyzed cyclization of lV-(2-iodoaryl)enaminones (equation 2) [31]. The latter were prepared from 2-haloanilines and a,p-ynones, which can react directly with 2-iodoaniline under the copper protocol to give 3-benzoyl-2-phenylindole (76%), thus bypassing the enaminone. Patel described a copper-catalyzed 3-aroylindole synthesis from 2-alkynylated... 

Isomerization of a, /S-unsaturated ynones into a,/3,y,6-unsaturated dienones in the presence of a Pd-PPhj complex promises to be of considerable synthetic utility. Some representative results are summarized in Table Curiously, however, the same research... 

In the similar iodocyclization of a-amino ynones 41 (Scheme 24), PEG MOO was a less effective solvent and better yields of 42 were obtained at room temperature with acetonitrile as a solvent [47]. However, the a-amino ynones 41 underwent 5-endo-dig cycloisomerization in PEG 3400 rmder microwave irradiation in the presence of platinmn(ll) chloride affording pyrrolin-3-ones 43 [48]. In the presence of potassium carbonate, the reaction proceeded without substantial epimerization of the products 43. The recyclability of tiie catalytic system and PEG 3400 was also investigated. 

A new procedure for the synthesis of large-ring or,/3-ynones involves the intramolecular acylation of readily accessible [Pg.39]

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