Lactones, preparation from keto-esters

It is remarkable that the hydrosilylation procedure has been successfully used for the synthesis of important targets. Matsumara and co-workers demonstrated the applicability of their developed method in the preparation of optically active lactone 109 from keto ester 108 in 93 % yield with 97 % ee (Scheme 36) [215]. Lactone 109 is an important building block for the synthesis of a variety of biologically active substances [216-218]. 

Steric hindrances may also be the reason why quaternary salts of 8-alkylnarcotoline (130) were transformed during Hofmann degradation to analogous keto acids (131) (111,112) and not to the enol lactones (Scheme 24). In some cases (5,87) the keto acids and their esters have been synthesized from the corresponding enol lactones by hydration (Section III,A,2). Nornarceine (107) was prepared from JV-benzyl-(—)-a-narcotinium bromide (139, X = Br) by Hofmann degradation followed by N-debenzylation and ester hydrolysis (109). 

A highly selective method for the preparation of optically active 3-substituted or 3, y-disubstituted-S-keto esters and related compounds is based on asymmetric Michael additions of chiral hydrazones (156), derived from (5)-l-amino-2-methoxymethylpyrrolidine (SAMP) or its enantiomer (RAMP), to unsaturated esters (154).167-172 Overall, a carbonyl compound (153) is converted to the Michael adduct (155) as outlined in Scheme 55. The actual asymmetric 1,4-addition of the lithiated hydrazone affords the adduct (157) with virtually complete diastereoselection in a variety of cases (Table 3). Some of the products were used for the synthesis of pheromones,169 others were converted to 8-lactones.170 The Michael acceptor (158) also reacts selectively with SAMP hydrazones.171 Tetrahydroquinolindiones of type (159) are prepared from cyclic 1,3-diketones via SAMP derivatives like (160), as indicated in Scheme 56.172... 

In the event, iodolactonization of the carboxylate salt derived from the ester 458 afforded 459, and subsequent warming of the iodo lactone 459 with aqueous alkali generated an intermediate epoxy acid salt, which suffered sequential nucleophilic opening of the epoxide moiety followed by relactonization on treatment with methanol and boron trifluoride to deliver the methoxy lactone 460. Saponification of the lactone function in 460 followed by esterification of the resulting carboxylate salt with p-bromophenacylbromide in DMF and subsequent mesylation with methanesulfonyl chloride in pyridine provided 461. The diazoketone 462 was prepared from 461 by careful saponification of the ester moiety using powdered potassium hydroxide in THF followed by reaction with thionyl chloride and then excess diazomethane. Completion of the D ring by cyclization of 462 to the keto lactam 463 occurred spontaneously on treatment of 462 with dry hydrogen chloride. 

D-Erythroascorbic acid (D-g/vccro-2-pentenono-1,4-lactone, 142), was prepared from D-glucose by degradative oxidation to potassium D-arabinonate, which was acidified and lactonized. The lactone 143 was converted in one step into the 2-keto methyl ester 144, which finally was tautomerized in hot methanolic sodium acetate, affording D-erythroascorbic acid (142) as a crystalline solid.328... 

The methoxyketene 297, coordinated to Cr carbonyl, is formed from methoxy-carbene easily by insertion of CO under irradiation [90]. An ester is formed by the reaction of ketene with alcohol. The aminocarbene complex 298 was prepared from benzamide and converted to phenylalanine ester 300 under irradiation of sunlight in alcohol via ketene 299 [91]. The eight-membered lactone 304 was prepared in high yield by the reaction of the alkyne 301 having the OH group in a tether with Cr carbene without irradiation. The vinylcarbene 302 is formed at first and converted to the vinylketene intermediate 303 as expected. The keto lactone 304 is formed from 303 by intramolecular reaction with the OH group and hydrolysis [92],... 

Substitution of one of the ester groups for another functional group may also allow one mode of cyclization to occur. Where cyanide replaces one of the esters, cyclization occurs from the cyano-stabilized anion. Seven-membered (e.g. 60) and heterocyclic (e.g. 61) rings - can be prepared regio-selectively. In competition between an ester and the PhS02-stabilized anion the latter cyclizes even where it is secondary and the ester is primary, (62) to (63), presumably in part a reflection on the electro-philicity of the two groups and the stabilities of the products. The ester lactone (64) cyclizes to the keto ester (65) involving the enolate of the lactone, but cyclization in the opposite sense is sterically unlikely (Scheme 28). ... 

Asymmetric hydroxylation of etiolates. Davis and Chen1 have reviewed this reaction using in particular (R,R)- and (S,S)-2-phenylsulfonyl)-3-phcnyloxaziridene (1) and (camphorylsulfonyl)oxaziridine (2). Of these reagents, 1 and ( + )- and (—)-2, derived from (lR)-lO-camphorsulfonic acid, provide highest enantioselectivity and in addition are easy to prepare. They are effective for hydroxylatation of ketones, esters, /2-keto esters, amides, lactones, and lactams. 

The enantiomerically pure 2,3-unsaturated aldonic lactone 2 was prepared following Sharpless asymmetric dihydroxylation of 2-vinylfuran to give 1 (Scheme 1). The chain-extended aldonolactones 4 and 5 were prepared from the P-keto ester 3 by use of a diastereoselective reduction with either d- or L-tartaric acid in conjuction with sodium borohydride (Scheme 2). Reaction of Meldrum s acid (5a) with D-aldopentoses and hexoses gave 3,6-anhydro-2-deoxy-aldono-... 

Derivatives of Y-hydroxyacetylenic acids, which are useful intermediates in the synthesis of butenolides, are prepared from propiolic acid and ester anions. Alk-2-ynoic and 2-allenic esters are prepared by the oxidation of 3,4-disubstituted 2-pyrazolin-5-ones with lead(iv) tetra-acetate in the absence and presence of BF3 respectively. Py-Unsaturated esters are produced in high yield by the palladium-catalysed decarboxylation-carbonylation of allylic carbonates. Magnesium enolates of esters react with nitriles to give (Z)-3-amino-alk-2-enoates. Enol lactones react with diethyl methoxycarbonylmethylphosphonate to give cyclic unsaturated keto-esters (Scheme 66). ... 

Aeylaerylic esters structures from /3-keto sulfoxides by reaction of methyl esters with dimsyl-potassium (method of Corey, 1, 311). The steps are outlined in equations (1) and (II). This method was used to prepare the isocardenolide 3 acetoxy-20-hydroxy-21-nor-5,22-choladiene-24-oic acid y-lactone from methyl 3)J-hydroxy-ctienate in excellent yield. 

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 . ... 

In compounds of this group, the B ring of khivorin derivatives is opened to a lactone or ester, apparently by oxidation of a 7-keto compound, without the formation of any subsequent carbon ring. This has been done in the laboratory by Baeyer-Villiger oxidation and andirobin (37) has been partially synthesised (74, 76) (Scheme 6). When a suitable derivative is prepared, cyclisation occurs spontaneously to give a l,14 oxide this can be formed from either a -hydroxy or a 14-hydroxy compound... 

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