Olefins monoactivated

Little has investigated monoactivated and doubly activated alkenes tethered to butenolide with respect to electroreductive cyclization [202]. The geminally activated systems 227 undergo cyclization to diastereomeric products 228 and 229 in an 1 1 mixture, whereas both the a,j8-unsaturated monoester and a,/ -unsaturated mononitrile fail to cyclize. Only saturation of the C-C double bond of butenolide is observed. The author explains these results by distinct reactivity and lifetime of the intermediate radical anions. The radical anions derived from the monoactivated olefins are less delocalized than those of 227 and therefore should be shorter lived and more reactive. In this case preferential saturation occurs. The radical anions derived from the doubly activated alkene 227 are comparatively long-lived and less basic and thus capable of attacking the C-C double bond of the butenolide moiety. A decrease in saturation, accompanied by a marked increase in cyclization, is observed. 

The Z-isomers of monoactivated olefins may be more easily reduced than the E-isomers in aqueous solutions, but no significant differences are observed in nonaqueous media [540-543]. 

A methylsulfido substituent on the furan significantly enhances its reactivity toward dienophiles. Therefore, cycloadditions of 3-methylthiofuran proceeds even with monoactivated olefins to give predominantly the endo adducts, Eq. 6 [18]. Moreover, chiral titanium catalysts generated in situ from (z-PrO)2TiCl2 and tartrate derivative 9, Fig. 2, induce cycloaddition with 3-acryloyl-l,3-oxazo-lidin-2-one with good enantioselectivity and in excellent yield, Eq. 7. 

Gas volumetric measurements show that tetraethyl ammonium cyanide takes up one molar equivalent of carbon dioxide giving a probable cyanoformate intermediate (88) although evidence for its structure was not obtained. The complex (88) adds to monoactivated olefins to give the salts (89) which can be alkylated to the corresponding esters. The overall transformation is of cyanocarboxylation. The reaction is not successful with doubly activated olefins because of competing... 

A comprehensive study of the addition of monoactivated olefins to nitronic esters has been described by Gree et this work provides a useful synthesis... 

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