Structure and Chemistry of Malonylmethyl‐ and Succinyl‐Radicals. The search for homolytic 1,2‐rearrangements

Abstract

SummaryMalonylmethyl radical I [. CH,CH(COOE:t),] and its thioester analogue I1 [. CH,CH(COOEt) (COSEt)] were generated by standard photolytic and thermolytic methods from perester and bromo precursors. The structures of I and I1 were examined by ESR spectroscopy and found to exist in preferred conformations. However, no indication for their rearrangement by 1,2-shift of either an ethoxycarboxyl or (ethylthio)carbonyl group to the corresponding succinyl radicals I11 and IV, respectively, was found at temperatures below -40 "C. At higher temperatures of up to 140 "C, the search for malonylmethyl -+ succinyl rearrangement was examined by thorough-product analysis of the perester decomposition. There is evidence for the rearrangement of the radical I to I11 by photolysis and of the radical I1 to IV by thermolysis at 130 "C in chlorobenzene to only a small extent.

Effect of Supramolecular Inclusion on the 1,2-Rearrangement of Free Radicals

“…Only very small amounts of rearranged product 6 (2.2%) were detected in the irradiation experiment with 3, while none was found in the corresponding experiment with 4. These results are in agreement with the work of Keese×s group [11] who found 1.7% of rearrangement product upon photolysis of 3 in cyclohexane.…”

“…and 2 . , the peresters tert-butyl 4-ethoxy-3-(ethoxycarbonyl)-4-oxobutaneperoxoate (3) [11] and its 3-methyl derivative 4 were prepared (Scheme 2). The expected products were in part commercially available and characterized by NMR spectroscopy and elemental analysis.…”

“…The expected products were in part commercially available and characterized by NMR spectroscopy and elemental analysis. All were identified by GC/ MS. Photoirradiation of the peresters 3 [11] and 4 was carried out in a quartz vessel at room temperature with a low-pressure Hg lamp. Upon irradiation, 3 and 4 underwent homolytic cleavage with concomitant decarboxylation, generating a tert-butoxy radical and radicals 1 .…”

Dual Hypervalent Iodine(III) Reagents and Photoredox Catalysis Enable Decarboxylative Ynonylation under Mild Conditions

“…We also carried out 13 Ci sotopic-labeling experiments to explore how the acyl radical added to the BI-alkyne.B yu sing the 13 C-labled BIalkyne 55,w ef ound exclusive 13 Cr etention in 56,w hich was formed in 70 %yield. As the migration of the ester group was generally difficult, [21] a b-addition followed by an exclusive ester migration was unlikely (bottom equation in Scheme 2d), thus an a-addition [22] accompanied by benziodoxole radical elimination was suggested (top equation in Scheme 2d).…”

“…Heterocyclic thiophenes,f urans,a nd indoles reacted smoothly to give ynones [17][18][19].N otably,a lkyl-substituted ketoacids decarboxylated to give coupling adducts:P rimary and secondary alkyl ketoacids gave ynones without decarbonylation in 66 %a nd 82 % yields,r espectively (20,21), while the tertiary alkyl ketoacid gave the dual decarboxylative-decarbonylative alkyne coupling adduct 22 in 73 %y ield. [15] In addition to aryl-and alkyl-substituted a-ketoacids,c arbamoyl ketoacids readily reacted to give ynamides:P rimary carbamoyl ketoacids reacted to give,inyields of 61-69 %, primary ynamide products, which could not be obtained by transition-metalcatalyzed aminocarbonylation because of the catalytic inhibition of primary amines by transition metals (23)(24)(25)(26)(27)(28).…”