5-Methylene-2 -furanone, formation

Those 3(2//)-furanones with a methylene group at the 2-position condense with ethyl formate and amines to give aminomethylene derivatives of type 46. In such compounds the heterocyclic ring is easily opened by nucleophiles because the functional grouping is that of a vinylogous ester with amines,... 

First, a simplified model of DNA, polydeoxyadenylic acid, was shown to be readily cleaved at neutral pH by Mn-TMPyP/KHSOs with spontaneous release of free adenine and, after heating, formation of a rather unstable sugar degradation product identified as 5-methylene-2(5H)-furanone, supporting a C-1 oxidation pathway. The first /3-elimination created a 5 -phosphate end and the second one was accompanied by 5-MF release. The two DNA strands were terminated by phosphate groups (Fig. 6, route A) (282). 

Binger and Weintz studied the reaction of the unsubstituted methylene-cyclopropane with carbon dioxide and obtained the 3-methy1-2-buten-4-olide in yields up to 80 % [25,26]. As shown in Figure 10, parallel to the main reaction, the formation of cotrimers, cotetramers and copentamers can not be avoided. A mechanism is proposed, in which the palladium forms a trimethylenemethane intermediate which exists in two tautomeric structures (Figure 11). By insertion of carbon dioxide palladium carboxylate complexes are formed which release the furanone. 

A general and mild method of preparation of 5-methylene-2(5 T)-furanones has been demonstrated which involves (a) the formation and alkylation of the dianion (22) of 2-(methylthio)pent-4-enoic acid (21), (6) cyclization followed by dehydrosulphenylation, and (c) dehydroiodination, as shown in Scheme 1. 

The possibility of a biradical mechanism has been considered for the dimerization of butadiene. For this reaction CASSCF calculations predict the two-step mechanism as the most favorable one by 1.3 kcal mol . The stability of birad-icaloid structures is probably overestimated at this level of calculation, but the size of the system makes difficult the use of higher level ab initio methods. The biradical mechanism has also been explored for the reaction between protoanemonin (5-methylene-2(5//)-furanone) (4) and butadiene. In this system a multistep mechanism, involving the formation of 2 - - 2 adducts in the early stages of the reaction, has been found to be the most favorable one. These results are in excellent agreement with the experimental observations. 

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