Atom transfer radical cyclization (ATRC) of N-alkyl Nallyl dichloroamides to g-lactams, catalyzed by 'naked' CuCl, worked efficiently in DMF, whereas, when the same dichloroamides were N-sulfonylated, DMF needed to be replaced by acetonitrile. The outcome of the cycloisomerization with N-substituted N-allyl trichloroacetamides was less affected by solvent choice, although for an effective reaction to occur, the solvent had to dissolve the cuprous salt. Catalyst loading ranged between 5 and 20 mol%.
An efficient procedure for highly chemo- and stereoselective cyclization of (S)-allylalanine derivatives is reported (diastereomeric ratios up to 96:4) where the reaction course can be completely controlled by switching from gamma-lactones to cyclic carbamates simply with the proper choice of the amino acid protecting groups. Both processes are stereoconvergent and afford the (S,S)-products in high yields, short reaction times, and mild reaction conditions.
The preparation of the 3,4-dialkyl-substituted maleic anhydride nucleus, through the functional rearrangement of dichloro g-lactams, allowed the comparison of various N-substituents in the functional rearrangement step. The 2-pyridyl group proved to be the most appropriate N-substituent for the hydrolysis of the 5-methoxy-1,5-dihydro-2H-pyrrol-2-one intermediate into the 5-hydroxy adduct, and for the hydrolysis of the maleimide nucleus into the maleic anhydride. The oxidation of the 5-hydroxy-1,5-dihydro-2Hpyrrol-2-one into the corresponding maleimide was achieved with manganese(IV) oxide.
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