Acetylenic lactones from

Gold intramolecular processes are also possible. Using AuCl and K2C03 as catalysts, Harkat et al. achieved y- and 8-alkylidene lactonizations from co-acetylenic acids by efficient and stereoselective reactions [91]. 

In a chemical investigation of B. paniculata from Northern Chile, two isomer acetylenic lactones were isolated [30], while the aerial parts of B. salicifolia yielded two prenyl derivatives, Fig. (54) [21],... 

A large number of compounds, which are typical constituents of the Baccharis genus, were isolated from these species and might be partly or wholly responsible for the antimicrobial effects exhibited by the plants. For example, four compounds, including a flavone, an acetylenic lactone, a... 

Dilithium tetrachlorocuprate is recommended as an additive for cross coupling of Grignard compounds with tosylates even allylic and benzylic acetates give good yields . a-Methylene-ketones, -carboxylic acids and -lactones have been prepared via sulfides and sulfoxides. A convenient and general synthesis of acetylene derivatives from boranes via the reaction of iodine with lithium 1-alkynyltriorganoborates has been published ar-Nitrostyrenes can be easily obtained by a Wittig synthesis with formaldehyde in an aqueous medium . A new synthesis of unsym. ketones by reaction of dialkyldiloroboranes with lithium aldimines has recently been published . Metallo aldimines have also served for the synthesis of a variety of other compound classes such as a-hydroxyketones, a-keto acids, nitriles, and for the asym. synthesis of a-amino acids . Polycondensations of malononitriles with benzylic chlorides have been carried out quantitatively under mild conditions in dimethyl sulfoxide with triethylamine as acid acceptor . Carbonyl compounds can react with dibromoacetonitrile to yield a-bromo esters with additional carbon atom . ... 

Suitable catalysts for ring closure reactions are cobalt carbonyls [123, 280, 673, 674], rhodium carbonyls [280, 678], iron carbonyl [123] and certain palladium compounds [679]. Nickel carbonyls, the active catalysts in the Reppe syntheses, are inactive in most cases [123, 673]. A few examples in which nickel is active are the formation of phenols from allyl halides, acetylene and carbon monoxide, which is only a side reaction, and the mechanistically unclear formation of lactones from allyl carbinol and bu-tyne-l-ol-4 [438]. 

Lactones from Acid Halides, Acetylene and Carbon Monoxide... 

An insight into the mechanism of metal-catalysed formation of lactones from acetylenes, carbon monoxide, and alkyl, allyl, or aryl halides is provided by the reactions of [MRCCOaC -CsHs)] (M = Mo or W R=Me, CHjPh, or COCFs) which indicate that migration of the R group on to co-ordinated CO is followed by acetylene insertion and to give (1) (Scheme 1). The second CO insertion leading to the... 

Simple olefins do not usually add well to ketenes except to ketoketenes and halogenated ketenes. Mild Lewis acids as well as bases often increase the rate of the cyclo addition. The cycloaddition of ketenes to acetylenes yields cyclobutenones. The cycloaddition of ketenes to aldehydes and ketones yields oxetanones. The reaction can also be base-cataly2ed if the reactant contains electron-poor carbonyl bonds. Optically active bases lead to chiral lactones (41—43). The dimerization of the ketene itself is the main competing reaction. This process precludes the parent compound ketene from many [2 + 2] cyclo additions. Intramolecular cycloaddition reactions of ketenes are known and have been reviewed (7). 

Chiral lactones were also obtained by cyclocarbonylation of chiral acetylenic alcohols with Pd and thiourea (H2NCSNH2) (Scheme 32). No loss in chirality was observed, but large amounts of Pd and thiourea were used (10 mol %) since the catalyst deactivates by forming metal particles. The catalytic precursor (Pdl2 > PdCl2) and the ratio of thiourea to Pd were very important, thiourea being necessary for this reaction. The active species was supposed to be [Pd(thiourea)3l]I, which forms in situ from [Pd(thiourea)4]l2 and [Pd(thiourea)2]l2. It had to be a partially dissociated species since [Pd(thiourea)4](Bp4)2 was inactive [121]. 

W=X is N=N or C=N, never if it is C=C. The ring stability of 3-furyl-carbenes conforms with this rule. Ring opening is again the main reaction in a biradical which is generated by extruding carbon dioxide from a lactone at 675°C and which then collapses to an acetylenic ketone.277... 

The utility of the creation of a y-lactone enolate through 1,4-addition of a carbanion and its interception by an electrophile has also been demonstrated in other classes of natural products, e.g., in the enantioselective synthesis of 10-oxa-l 1-methyl PGE2 analogues22. This synthesis starts with 1,4-addition of the sulfone-stabilized anion from 27 to ( + )-(S )-4-methyl-2-buteno-lide which has been prepared in three steps from (—)-(S)-l,2-epoxypropane. The intermediate enolate 28 is reacted with the acetylenic iodide to give the trisubstituted diastereomeric mixture of lactones 29, which is eventually converted into the pure compound 30, both reactions occurring with high diastereoselectivity. 

Only seven of the nine carbonyl groups can be liberated as carbon monoxide, indicating that two carbonyl groups have combined with the acetylene to form a new ligand. X-ray studies on the complex derived from acetylene show that the complex contains an unsaturated lactone ring as shown in (LXIII) (160). An important structural feature of (LXIII) is that the... 

The dianion derived from but-2-ynoic acid reacts with aldehydes to give 5-hydroxyalk-2-ynoates (539). Partial reduction over a Lindlar catalyst and acid-catalyzed cyclization of the resulting enoate gives the dihydropyran-2-one (78LA337). The route is exemplified by the synthesis of the naturally occurring massoia lactone (Scheme 200). In previous work (46JCS954) the hydroxyalkynoic acids themselves, obtained from epoxides and acetylene, were used. 

The second method of preparation (shown in Scheme 2) depends on treating dehydroepiandrosterone (prepared from cholestrol or sitosterol) with acetylene to form the 17a-ethnyl-17p-hydroxy derivative, which is carbonated to the 17a-propionic acid. Reduction of the unsaturated acid in alkaline solution yields the saturated acid, which cyclizes to the lactone on acidification. Bromination to the 5,6-dibromo-compound, followed by oxidation of the hydroxyl group to the ketone, and then dehydro-bromination to the 7a-hydroxyl derivative, produces spironolactone when esterified with thiolacetic acid. 

Very recently, new ruthenium catalysts, for example RuCl2(triazol-5-ylidene) (p-cymene) [11] and the catalytic system generated in situ from [RuCl2(p-cym-ene)]2, tris(p-chlorophenyl)phosphine, and 4-dimethylaminopyridine [12], have provided efficient catalysts for synthesis of the same type of enol ester. The regio-selective cyclization of acetylenic acids containing a terminal triple bond to give unsaturated lactones was performed in the presence of catalytic amounts of Ru(tris(pyrazolyl)borate)(PhC=C(Ph)C CPh)(PMe2iPr2) [13],... 

Enol lactonization. The last step in a synthesis of ( )-cyanobacterin (2), an antibiotic isolated from a cyanobacterium, is the enol lactonization of the y,8-acetylenic carboxylic acid 1. Cyclization catalyzed by AgNO, results in the desired exocyclic y-... 

Of more specialized interest is the reaction of alkynes with Co2(CO)s in polar solvents under conditions of elevated temperature and CO pressure. The major products are the (E) and (Z) isomers of so-called bifurandiones, the products of formal (but not actual) carbene dimerization. An intermediate, a complex of this lactone-derived carbene bridging a Co2(CO>7 moiety, may be isolated from reactions of alkyl-, aryl- or dialkyl-acetylenes with Co2(CO)8. Its formation is completely regioselective even for ethyl vj. methyl, placing the larger group a to the lactone carbonyl. - In the subsequent formation of the bifurandione itself regioselectivity in alkyne incorporation into the second ring is incomplete and in the opposite direction, an observation which remains unexplained (Scheme 11). ... 

Alcohols can undergo photoaddition to alkynes, and the products from acetylenic esters are Y-hydroxy-rra//j-a,j3-unsaturated esters or the unsaturated lactones derived from the cis isomers by cyclization (equation 21). Reaction with acetylenic ketones provides a route to furans (equation 22) , and there is n.m.r. evidence for... 

Since the importance of sesquiterpenes, sesquiterpene lactones and flavonoids from the chemosystematic and the biological point of views, especially the chemistry and the biological activities of these compounds will be reviewed in this chapter, while the essential oils and the acetylenic compounds will not be mentioned. 

The strategy is based on the pseudo C2-symmetric feature of the target. Lactone 26 prepared from D-arabinose, serves as the precursor of acetylenic derivative 27 and as the substrate in the... 

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