6-Lactones diastereoisomer complex

At the present time, the measurement of the enantiomeric excess of any given 3-lactone can be carried out by NMR spectroscopy. First of all, a diastereoisomer complex can be formed between the 3-lactone and S-2,2,2-trifluoro-(anthryl-9)-1-ethanol, as suggested by Pirkle et al. However, this method often requires a high-field NMR apparatus ( 250 MHz in proton), but it gives results which are consistent with those obtained... 

Viridifloric /3-lactone, 143, has been identified as one of the pheromone components of a complex mixture of volatiles released by the pheromone glands of the male Idea leuconoe butterfly during courtship <1996BMC341>. A racemic mixture of both diastereoisomers was synthesized in four steps from the dilithio salt of 3-methylbutyric acid 144 alkylation with ethanal, dehydration of the secondary alcohol with phosphorus pentoxide, dihydroxylation of the C-C double bond with osmium tetraoxide, and finally formation of the /3-lactone by cyclization with sulfonyl chloride. By comparison with the sample isolated from I. leuconoe, the absolute configuration was established to be (2V,3V)-2-hydroxy-2-(l-methylethyl)-3-butanolide 143. 

The deMayo-type photochemistry of 1,3-dioxin-4-ones has been beautifully applied by Winkler et al. to the synthesis of complex natural products. Substrate 133 gave under sensitized irradiation (with acetone as cosolvent) product 134 as single diastereoisomer (Scheme 6.47). The diastereoselectivity results from cyclic stereocontrol exerted by the two stereogenic centers in the spiro-bis-lactone part of the starting material. After installation of the furan, saponification and bond scission in a retro-aldol fashion generated a keto carboxylic add, which produced the natural product ( )-saudin (135) by simultaneous formation of two acetal groups [128]. 

For example, coupling of complexed aldehyde 31 with ethyl acrylate gave lactone 32 with complete diastereocontrol.52 Furthermore, Lewis acid-mediated epimerisation of lactone 32 allowed for the isolation of the alternative diastereoisomer 33. Subsequent decomplexation with iodine liberated the two enantiomerically pure lactones.52... 

Studies have been made of the photochemical reactions of vinyloxiranes with iron carbonyl. The four diastereoisomers of 2,4-hexadienemonooxirane take part in photochemical reactions that are stereospecific. The structure of the iron complex has been determined by x-ray crystallography. Complexes formed from dienemonooxiranes with iron carbonyl can be oxidized to lactones. ... 

A detailed investigation was later reported by Frontier in which a conrotatory electrocyclization of silyloxyfurans 79 was catalyzed by the same Ir(III) complex (76) to produce lactones 80 in good yield. This work culminated in the total synthesis of racemic merrilactone A (83) (Scheme 3.18) [21]. Generally, only one diastereoisomer was isolated from the Nazarov reaction. These cyclizations also demonstrated complete transfer of the trialkylsilyl group from the silyloxyfuran to the ketone oxygen. It had been previously demonstrated that trialkylsilyl species can catalyze the Nazarov reaction further experiments showed that although... 

The reaction can be carried out under photolytical conditions applying pentacarbonyliron. More frequently, however, nonacarbonyldiiron is employed that does not require irradiation. The reaction is typically carried out in tetrahydrofuran at room temperature. The allyliron complex obtained is part of a ferralactone ring system that after demetalation is transformed to give P or 6-lactones (Scheme 4-82). The formation of ferralactone complexes is a multistep process. This can be concluded from its stereochemical outcome. The relative configuration of the oxirane ring of Cl-monosubstituted vinyloxiranes is not preserved in the course of the reaction, but a mixture of four possible diastereoisomers can be obtained exo,cis exo,trans endo,cis endojrans Scheme 4-83). In most cases, cis-products are formed with respect to the position of the allyl moiety. 

---