Silver nitrate, ring closure with

As discussed in Section 10.3, the system consisting of a diazonium ion and cuprous ions can be used for hydroxy-de-diazoniation at room temperature in the presence of large concentrations of hydrated cupric ions (Cohen et al., 1977 see Schemes 10-7 to 10-9). With (Z)-stilbene-2-diazonium tetrafluoroborate under these conditions, however, the major product of ring closure of the initially formed radical was phenanthrene (64%). When the cupric nitrate was supplemented by silver nitrate the yield increased to 86% phenanthrene. Apparently, the radical undergoes such rapid ring closure that no electron transfer to the cupric ion takes place. 

The cyclization of 5,6-alkadienylamines with silver nitrate in water/acetone (50 50) at 60 CC gave 2,6-disubstituted piperidines 7, although the stereoselectivity of the ring closure is not high108. 

A very interesting example of a highly stereoselective thermal 671-disrotatory ring closure is a result of the work of Benson and West (Scheme 19.5). Reduction of dienyne 13 at room temperature with zinc that had been activated by successive treatments with copper(ll) acetate and silver nitrate in a mixed solvent of tetrahydrofuran (THF) and water at room temperature led to diene 15 as a single isomer in 67% yield after 11 days. The electrocyclization presumably proceeds through the intermediacy of triene 14. At higher reaction temperatures, Z to isomerization of the triene competed with the cyclization. Product 15 was also... 

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