P-Alkynyl ketones

ASYMMETRIC REDUCTION OF PROCHIRAL a, P-ALKYNYL KETONES TABLE 21.1 a-Pinene-9-BBN Complex... 

The first palladium-catalyzed conjugate addition of terminal alkynes to a, 8-unsaturatedenones has been reported. The reaction, which can be carried out in either water or acetone, affords p-alkynyl ketones in high yields (eq llO). ... 

Recently the Bohlmann-Rahtz synthesis has received greater attention. Baldwin has employed this method for the construction of heterocyclic substituted a-amino acids. Exposure of alkynyl ketone 39 to 3-aminocrotoyl ester 40 resulted in the Michael product 41. Thermolysis then gave rise to the desired pyridyl-P-alanines 42. 

Treatment of 210 under traditional Eschenmoser fragmentation conditions gave only low yields of the desired alkynyl ketone 211, but this result was improved significantly by use of p-nitrobenzenesulfonylhydrazine in place of the commonly used p- lolueriesul fonylhydrazine. Compound 211 was transformed into the bis-oxime 212, reductive cyclization of which by treatment with ZrCU and NaBH4 and subsequent acylation afforded the polycyclic compound 213 with the desired all-cis... 

The add-catalyzed cyclodehydration of (Z)- and ( )-6-hydroxy-a,p-unsaturared ketones offers a mild synthesis of substituted furans. In the case of ( )-olefins, photochemical isomerisation was found to accelerate the reaction <96TL6065>. Reaction of alkynyl(phenyl)iodonium tetrafluoroborates with tropolone in the presence of a base yields 2-substituted furotropones (Scheme 16, <96TL5539>). 

Cyclocondensation processes of p-dicarbonyl derivatives or their analogues are still widely employed for the synthesis of new isoxazoles. Non-proteinogenic heterocyclic substituted ct-amino acids have been synthesised using the alkynyl ketone functionality as a versatile building block ynone 2, derived from protected L-aspartic acid 1, reacted with hydroxylamine hydrochloride affording the isoxazole 3 with enantiomeric purity greater than 98% ee <00 JCS(P 1 )2311 >. 

E,E)-a,P Y,5-Drenones.2 Aryl a,(3-alkynyl ketones rearrange in the presence of this ruthenium catalyst in refluxing toluene to conjugated (E,E)-dienones in 75-85% yield. A similar rearrangement with alkyl a,(i-alkynyl ketones proceeds less readily. 

In addition, iodine snccessfnlly catalyzed the electrophilic snbstitntion reaction of indoles with aldehydes and ketones to bis(indonyl)methanes [225], the deprotection of aromatic acetates [226], esterifications [227], transesterifications [227], the chemoselective thioacetalization of carbon functions [228], the addition of mercaptans to a,P-nnsatnrated carboxylic acids [229], the imino-Diels-Alder reaction [230], the synthesis of iV-Boc protected amines [231], the preparation of alkynyl sngars from D-glycals [232], the preparation of methyl bisnlfate [233], and the synthesis of P-acetamido ketones from aromatic aldehydes, enolizable ketones or ketoesters and acetonitrile [234],... 

Conjugate addition of alkynylboiates to a,P-unsatuiated ketones, followed by acid-catalyzed cyclization of the resulting y-alkynyl ketones afforded trisubstituted fiiians in moderate to high yields <99T14233>. 

Intramolecular 2 + 2 + 2-cycloisomerizations of cyclic triynes and enediynes have been reported with RhCl(CO)(PPh3)2.126 The transition metal-catalysed rearrangement of alk-5-ynals to /-alkynyl ketones and cyclopent-l-enyl ketones was developed using [Rh(P(OPh)3)2]BF4 or Cu(OTf)2 as a catalyst and the effect of substituents on the partition to products was elaborated (Scheme 84).127... 

The conjugate addition of B-(l-alkynyl)-9-borabicyclo(3.3.1)nonanes (B-l-alkynyl-9-BBN) to a,P-unsaturated ketones provides a convenient procedure for the preparation of y,8-acetylenic ketones81) (Eq. 35). Cuprous methyltrialkylborates react... 

An asymmetric reducing agent (49), prepared from LAH, (-)-)V-methylephedrine (14) and 3,5-di-methylphenol in a 1 1 2 ratio, reduces acetophenone with 83.8% A series of aromatic and alkynyl ketones are reduced by (49) to the corresponding (f )-alcohols (Scheme 1)P Some of the products are useful intermediates for the synthesis of 7-lactone insect pheromones. " ... 

Simple a,3-unsaturated aldehydes, ketones, and esters (R = C02Me H > alkyl, aryl OR equation 1)13 preferentially participate in LUMOdiene-controlled Diels-Alder reactions with electron-rich, strained, and select simple alkene and alkyne dienophiles, although the thermal reaction conditions required are relatively harsh (150-250 C) and the reactions are characterized by the competitive dimerization and polymerization of the 1-oxa-1,3-butadiene. Typical dienophiles have included enol ethers, thioenol ethers, alkynyl ethers, ketene acetals, enamines, ynamines, ketene aminals, and selected simple alkenes representative examples are detailed in Table 2. The most extensively studied reaction in the series is the [4 -t- 2] cycloaddition reaction of a,P-unsaturated ketones with enol ethers and Desimoni,... 

Variations on this theme include the use, as synthons for the 1,3-dicarbonyl component, of P-chloro-a,P-unsaturated ketones, or of conjugated alkynyl aldehydes. ... 

Other synthons for 1,3-dicarbonyl compounds that have been successfully applied include p-chloro-a,P-unsaturated ketones and aldehydes, P-dimethylamino-a,P-unsaturated ketones (easily obtained from ketones by reaction with DMFDMA), P-alkoxy-enones"" and vinyl-amidinium salts."" Alkynyl-ketones react with 5-alkyl-isothioureas, giving 2-alkylthio-pyrimidines" and propiolic acid reacts with urea to give uracil directly in about 50% yield. "" 1,3-Keto-esters with formamidine produce 4-pyrimidinones"" and C-substituted formamidines with ethyl cyanoacetate give 2-substituted-6-amino -pyrimidinones. In analogy, pyrimidines fused to other rings, for example as in quinazolines, can be made from ortho-aminonitriles " and in general, from P-enamino esters. ... 

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