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The stereoselective addition of chiral and achiral titanium enolates derived from the corresponding N-acyl oxazolidin-2-ones to 5- and 6- membered N-acyliminium ions afforded 2-substituted pyrrolidines in moderate to good diastereoisomeric ratio (5:1 to 14:1) while lower diastereoselection was generally observed in the formation of the corresponding 2-substituted piperidines. The stereochemical outcome was found to be modulated by the nature of the cyclic N-acyliminium ion (5- or 6-membered) and of its carbamate and by the N-acyl group in the enolate precursor. The preferential lk approach seems to be dictated mainly by the minimization of non-bonding interactions between the N-acyl group in the chlorotitanium (IV) enolate and the carbamate and methylene groups in the cyclic N-acyliminium ion.A adição estereosseletiva de enolatos de titânio derivados de N-aciloxazolidin-2-onas a ions N-acilimínios de 5- e 6-membros forneceu pirrolidinas 2-substituídas em proporção diastereoisomérica de moderada a boa (5:1-14:1) enquanto diastereosseletividade inferior foi observada na formação das piperidinas 2-substituídas correspondentes. O curso estereoquímico desta reação mostrou ser modulado pela natureza do ion N-acilimínio cíclico (5 ou 6 membros), pela natureza de seu grupo carbamato e do grupo N-acila presente no precursor do enolato. O modelo lk de aproximação parece ser dirigido pela minimização de interações de natureza não-ligante entre o grupo N-acila do enolato de titânio (IV) e os grupos carbamato e metilênico presentes no ion N-acilimínio

The stereochemistry of the addition of chlorotitanium enolates of N-acyl oxazolidin-2-ones to 5- and 6- membered N-acyliminium ions