3-Keto-8-lactones

The furo- and pyranobenzopyranones 114 and 115 are prepared by the reaction of 0-enolate of i(-keto lactone 113[132], The isoxazolc 117 is obtained by the oxidation of the oxime 116 of a, /3- or, d, 7-unsaturated ketones with PdCh and Na2C03 in dichloromethane[l 33], but the pyridine 118 is formed with PdCl2(Ph3P)2 and sodium phenoxide[134]. 

Again reductive opening of the lactone ring can be achieved at the chloro lactone or a,j5-unsaturated keto lactone stages. ... 

Another interesting conversion of a protoberberine to a rhoeadine skeleton was developed by Murugesan et al. (100). The ketol 176 obtained easily from berberine (15) (Section IV,A,2) was oxidized with sodium periodate to the keto lactone 451, which was transformed to the rhoeadine analogs 452 and 453 by known methods (Scheme 91). Their stereochemistry at the anomeric carbon was not fully clarified. 

Oxidative cleavage of P-hydroxyethers to keto-lactones was accomplished by RuClj/aq. Na(10 )/CCl -CH3CN thus hexahydro-benzofuran-3a-diol gave the corresponding nine-membered ketolactones (R =Me, Bu, R =H, Me Fig. 5.14) [87]. 

A stereoselective total synthesis of the antifungal mould metabolite ( )-LL-Z1271a (165) from the readily available Wieland-Miescher diketone, via the keto-lactone (164), has been described. A synthesis of grindelic acid (167) from the unsaturated 7-toluene-p-sulphonate (166) utilized an intramolecular solvolysis of the toluene-p-sulphonate to construct the 9—13 ether bridge. 

Myadera and Iwai (64CPB1338) have devised a convenient route to the bromide (139 R1 = R2 = R3 = H) starting with commercially available materials (Scheme 84). The anion formed from -y-butyrolactone by the action of sodium hydride was allowed to react with ethyl picolinate to yield the keto lactone (141) which, when heated with hydrobromic acid, undergoes decarboxylation as well as bromination, yielding the bromo ketone (139). Several substituted ethyl picolinates have been used successfully, and it has also been found that the anion of the keto lactone (141) may be alkylated. 

Treatment of 6-lithio-3,4-dihydro-2H-pyran (660) with the epoxy iodide (661) afforded the epoxydihydropyran (662). Compound (662) cyclized on exposure to basic A1203 to a single hydroxydihydropyran (663) which was oxidized with Collins reagent to the keto aldehyde (664) containing three contiguous asymmetric centers of fixed stereochemistry (Scheme 153). The metallated dihydropyrans have also found use in the construction of keto lactones (78JA7101). 

SL 358 (1995) (a-keto lactone and amide, a-amino ketone hydrochloride)... 

The procedure described is a simple, rapid, and convenient method for conversion of n-sized cycloalkenones into n+4 alkenolides. Significant but limited progress has been reported in the recent literature toward the preparation of medium and large ring lactones via ring-expansion reactions. One of the most notable and useful developments in this area involves conversion of a cycloalkanone into a bicyclic vinylic ether which is oxidatively cleaved to form a ring-enlarged keto lactone.3... 

The same catalyst effects asymmetric reduction of a-keto lactones (equation I)2 and -kelo carboxylates.3... 

The acylpalladium is formed by CO insertion as the intermediate of the carbonylation. They can be prepared directly by the oxidative addition of acyl chlorides to Pd(0). Thus ketones can be prepared by the reaction of acyl halides with organozinc reagents and organostannanes. Benzoacetate (490) is obtained by the reaction of benzoyl chloride with the Reformatsky reagent 489 [243], The macrocyclic keto lactone 492 is obtained by intramolecular reaction of the alkenylstannane with acyl chloride in 491 [244]. 

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],... 

After purification, the dimethyl 1,3-dioxinone unit of 2 was hydrolysed with mild base to furnish the P-keto acid. Acidification then brought about lactonisation to the enolised p-keto lactone 1. To facilitate work-up and isolation, the latter was converted to the vinylogous ester 24 with potassium carbonate and dimethylsulfate in acetone. Mild acid hydrolysis of 24 with 0.1 N H2S04 in EtOAc eventually furnished (-)-ACRL toxin 1 in good yield after six days, completing this very elegant and beautifully crafted synthesis. 

We next investigated the total synthesis of kuehneromycin A (7). Partial hydrolysis of 111 in trifluoroacetic acid (TFA) gave alcohol, which was oxidized to keto-lactone 112 (Scheme 18). Treatment of 112 with TFA followed by triethylamine caused unexpected decarboxylation, providing a mixture of kuehneromycin B (113) and panudial (114), which are known as natural products related to 7 [3]. The synthesis of... 

The present method has been successfully applied10 to the asymmetric reduction of various a-keto carboxylates and a-keto lactones. 

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