Wittig reaction with lactones

Reports of reactions of ylides with carbonyl compounds other than ketones and aldehydes continue to appear. Under extreme conditions lactones (66) undergo Wittig reactions with methoxycarbonylmethylene ylide, generally with... 

Treatment with dichloroacetyl chloride, followed by dechlorination of the resulting bicycloheptenone (177), produced the bicyclic ketone (178). Conversion into lactone (179) and reduction to (180) followed by Wittig reaction with propyl ylide produced cw-(181) selectively. The synthesis of (175) from (181) was then completed (- 0% overall yield) by oxidation to (182), isomerization to (183), followed by methylation and oxidation (Scheme 17). 

The pivalate was reductively removed at C25 using lithium triethylborohy-dride. It is notable that the lactone was not disturbed, perhaps an indication of the aforementioned steric congestion. Oxidation of the primary alcohol then gave aldehyde 36. A Wittig reaction with the phosphorane derived from 37 gave the Z-olefin and removal of the C9 protecting group completed the synthesis of lasonolide-A (1). 

In addition to its other properties, interest in the potential use of the vasodilative properties of prostaglandin El, alprostadil ( ), has led to several conceptually different syntheses.For this purpose, the classic Corey process has to be modified by reversing the order of addition of the side chains to allow for convenient removal of the unwanted double bond in the upper side chain. For example, Corey lactone is protected with dihydropyran (acid catalysis), reduced to the lactol with diisobutyaluminum hydride, and then subjected to the usual Wittig reaction to give intermediate This is... 

A furanose-fused c/.,(3-unsaturated 8-lactone was also prepared from ester 11 as a key chiral intermediate for the synthesis of the enantiomer of (+ )altholactone, a natural product with cytotoxic and antitumor activities.18 A Reformatsky reaction with ethylbromoacetate or a Wittig... 

Halo-lactonization of ketophosphoranes has been achieved via reaction with cyclic anhydrides and subsequent halogenation. " The products, halo enol lactones (75), are synthetically useful compounds, and an alternative synthesis via incorporation of the halogen at the ylid stage is also described. Mechanistic investigation of the Wittig reactions involved reveals subtle variations in pathway, allowing optimum experimental conditions to be selected to allow for the variation in reactivity of different anhydrides and halides. 

Baeyer-Villiger oxidation afforded the desired lactone 28 accompanied with hydro-xycarboxylic acid 29 as a byproduct. After removal of the acid 29, the lactone was reduced with DIBAL-H and employed in the Wittig reaction to form the PG structure 31 (Scheme 4). 

The author next tried to stabilize the PGI2 structure by introducing second fluorine atom to the 7-position. However, it had been unknown to make such a difluorovinyl ether unit in the literature. We studied difluorination and Wittig reaction as key steps in the synthetic route of the target difluoro-PGl2 from the Corey lactone. After searching the difluorination reaction, it was found that fluorination with A/-fluorobenzenesulfonimide in the presence of potassium bis(trimethylsilyl) amide and manganese dibromide effectively provided the desired difluoride (Table 7) [106]. 

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