Ring closure of y-haloamines

The radical intramolecular cyclization of a-anilino-oi-(chloromethylcarbonyl)phenylacetonitriles 150 is induced by tri- -butyltinhydride/azoisobutyronitrile to afford l-aryl-2-cyano-2-phenylazetidin-3-ones 151 (Equation 34) 1997JCM254 . 

Mitsunobu reactions have also been used for the cylization of 7-aminoalcohols toward azetidines. 7-Aminoalcohols 154, prepared from enantiopure ethynylaziridines, have been transformed into azetidines 155 upon treatment with dimethyl acetylenedicarboxylate and triphenylphosphine (Equation 35) 2001JOC1867 . N-Tosyl-substituted 7-aminoalcohols 156 yielded the corresponding 1-tosylazetidines 121 (Equation 36) with excellent diastereomeric (de = 99%) and enantiomeric excess (ee up to 99%) 2004EJ04471, 2005S3508 . 

Dehydrative cyclization of A-(4-methoxyphcnyl) protected 7-aminoalcohols 157 by the Staab reagent (1,1 -carbonyldiimidazole, CDI) led to the formation of iV-(4-methoxyphenyl)azetidines 158 (Equation 37) 2004SL2751 . The reactions were carried out in a Kugelrohr apparatus. The imidazole formed in the reaction was separated by filtration through silica gel. 

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