Azidoalkenes cyclizations

A simple cyclization was carried out to test the ability of chloro azidoalkene cyclization to generate quinolizidines. Reduction of 6-valerolactone to the corresponding lactol was followed by a Wittig reaction onto the carbonyl function employing an appropriate phosphonium salt, and the intermediate primary alcohol thus formed afforded the chloro... 

There have been a number of reports where alicyclic-bridged precursors underwent an IAAC reaction. Thus, the dioxolane (203b), formed from triflate (203a), cyclized in situ to a tricyclic triazoline (Scheme 63).113 Treatment of this triazoline with sodium ethoxide converted it to a diazopyrrolidine in 86% yield, which underwent smooth catalytic hydrogenation in 89% yield. The (Z)-azidoalkene (204), bridged by a (3-lactam, cyclized at 20 °C to triazoline (205).114 The triazoline (205) extruded nitrogen at 80 C providing a tricyclic aziridine. The ( )-isomer of (204) did not cyclize to a triazoline but instead produced an azirine, presumably via a nitrene intermediate. 

Piperidinecarboxylic acids, analogs of IV-acetylneuraminic acid, were synthesized by the re-gioselective intramolecular cycloadditions of the suitably substituted optically active azidoalke-nes 133,134. The best results were obtained when the substrate contained protected hydroxy functions. In the cyclization of tert-butyl 2-azido-6-heptenoates 17133, the diastereoselectivity is rationalized by analyzing the steric interactions in the transition states leading to the cycloadducts from different conformations of the azidoalkene. The cycloaddition took place on the / e-face of the alkenyl group in the chair transition state containing all axial substituents. 

Reductive Cyclization of (<>-Azidoalkenes. Hydroboration of < >-azidoalkenes with chloro(thexyl)borane followed by hydrolysis affords, via an intramolecular reductive cyclization, the corresponding p)UTolidine (78%) or the piperidine (53%) (eq 7). ... 

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