SYNTHESIS OF NEW 3,4-DISUBSTITUTED 2,5-DIHYDRO-1H-PYRROL-1-YLOXYL SPIN-LABEL REAGENTS VIA ALLYLIC REARRANGEMENTS

Several 3,4-disubstituted 2,5-dihydro-1H-pyrrol-1-yloxyl radicals were synthesized. roxymethyl-2,2,5,5-tetrameth-yl-1H-pyrrol-1-yloxyl radic al (1) was reacted with triethyl orthoacetate in a Claisen rearrangeme nt to give the exoolefinic compound 2. This was converted to its 1-ace toxyl derivative 3, which was then brominated in the allylic position. Subsequent rearrangement gave the endoolefinic compound hoxy-carbonyl methyl-2,2,5,5-tetramethyl-1H-pyrrole radical (4). The allylic bromine could be replaced with nucleophiles (NaSCN, KSeCN, thiourea, selenour ea, NaN3 and KSSO2Me) to give 5a-e and 26. The diamagnetic thiocyanate s and selenocyanates could be reduced with sodium borohydride to the f ree thiol and selenol monoradicals, which were oxidized to reversible, ester-functionalized disulfide or diselenide diradical reagents 24 an d 25.