Dimethyl dicarboxylate , carbonyl ylide

Heating organomercurial 34 resulted in the a-ehmination of phenyl mercury bromide, generating dichlorocarbene, followed by addition of benzaldehyde to form the corresponding carbonyl ylide 35. This ylide can be intercepted with dimethyl-acetylene dicarboxylate (DMAD) to produce dihydrofuran (36), which formed furan 37 through a dehydrochlorination process in 46% yield. 

In connection with this, dimethyl oxaquadricyclane-2,3-dicarboxylate (131) was initially assumed to behave as a carbonyl ylide 130 toward cy-clooctyne [81]. However, this proved to be not the case by an X-ray analysis of the adduct exo-132, but a first example of an inverse-electron demand [tt2 + a2 + o2 cycloaddition (Scheme 36) [82],... 

According to a recent report, however, the carbonyl ylides formed under these conditions may isomerize and lead to adducts different from those normally expected87. Thus, (5)-l-acetyl-2-(diazoacetyl)pyrrolidine (8). derived from /V-acetyl-i.-proline, upon treatment with dimethyl butynedioate in the presence of a catalytic amount of rhodium(II) acetate dimer at 25 °C affords only 10% of the expected adduct dimethyl 5,8-epoxy-2,3,5,8,9,9a-hexahydro-5-methyl-9-oxo-lH-pyrrolo[l, 2-o]azepine-6,7-dicarboxylate (9). Instead, dimethyl 1,2,8,9-tetrahydro-5-methyl-l-oxo-3a//,7//-furo[3,2-g]pyrrolizine-3a,4-dicarboxylate (10) is obtained in 87% yield. The formation of this product is explained via an isomeric ylide87 and thus occurs with complete loss of chiral information. 

Similarly, carbonyl ylide generated from the diazo compound in the presence of rhodium (II) acetate reacts with dimethyl acetylene dicarboxylate to give dihy-drofuran derivative [127]. 

We add an investigation of Chinese chemists to this section, although it is not related to carbenoid reagents that we have discussed above. Zhou et al. (1993) studied reactions of dimethyl diazomalonate and ethyl diazoacetate with carbonyl compounds mediated by diorganyl tellurides and catalytic amounts of cuprous iodide (8-69). Dibutyl telluride (8.155) yields the dimethyl l-arylethene-2,2-dicarboxylate 8.157 with 4-chlorobenzaldehyde in 95<7b yield at 100 °C. It is assumed that the reaction passes the telluronium ylide 8.156 as intermediate. If so, the process is clearly different from the carbenoid transformations discussed in this section. The originally diazo-substituted C-atom has nucleophilic character in 8.156 and is not electrophilic, as in 8.104. 

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