An expedient entry to the piperazinohydroisoquinoline ring system present in the tetrahydroisoquinoline antitumor alkaloids family is described. The synthetic sequence involves: a sequential Ugi reaction followed by an N-Boc-deprotection process and iminium formation with a spontaneous Pictet-Spengler cyclization and reductive N-methylation, with all these processes performed in a two-operation protocol in the same reaction flask.
To bypass the failure of radical cyclization involving a xanthate transfer on alkynes, a new reductive cyclization strategy has been completed with the use of a stoichiometric amount of dilauroyl peroxide in isopropanol. When the starting xanthates are prepared via a Ugi 4-component reaction with propargylamine, exomethylene lactams are formed in good yields.
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