Synthesis of new 3,4-disubstituted 2,5-dihydro-1H-pyrrol-1-yloxyl spin-label reagents via allylic rearrangements

Article abstract of DOI:10.1055/s-1993-25870

Several 3,4-disubstituted 2,5-dihydro-1H-pyrrol-1-yloxyl radicals were synthesized. 2,5-Dihydro-3-hydroxymethyl-2,2,5,5-tetramethyl-1H-pyrrol-1-yloxyl radical (1) was reacted with triethyl orthoacetate in a Claisen rearrangement to give the exoolefinic compound 2. This was converted to its 1-acetoxyl derivate 3, which was then brominated in the allylic position. Subsequent rearrangement gave the endoolefinic compound 1-acetoxyl-4-bromomethyl-3-ethoxy-carbonylmethyl-2,2,5,5-tetramethyl- 1H-pyrrole radical (4). The allylic bromine could be replaced with nucleophiles (NaSCN, KSeCN, thiourea, selenourea, NaN₃ and KSSO₂Me) to give 5a-e and 26. The diamagnetic thiocyanates and selenocyanates could be reduced with sodium borohydride to the free thiol and selenol monoradicals, which were oxidized to reversible, ester-functionalized disulfide or diselenide diradical reagents 24 and 25.