Chemistry of cis‐Trioxatris‐σ‐homobenzene. A Simple Total Synthesis of Streptamine

Abstract

step (1)-+(3) with methylmagnesium halide [R3=CH3 in (2)] are unsatisfactory, presumably because this relatively small reagent preferably adds to the ester carbonyl group.Experimental: All operations are carried out under nitrogen. A solution of (20 mmol) in light petroleum (20 ml) and ether (20 ml) is added dropwise over 30min to a stirred (magnetic stirrer) solution of (2) (40 mmol, prepared in situ from alkyl bromide and magnesium) in ether (50ml) (but not in tetrahydrof~ran"~) at -5°C. The addition product precipitates as a brown "tar" and should not be dissolved by addition of more solvent since otherwise (3) cannot be isolated. Stirring is continued for 30min at -5°C and the mixture is cooled with ice-water prior to addition of glacial acetic acid (40mmol) in water (50ml), whereupon the precipitate dissolves. The ethereal phase is separated off, the aqueous phase extracted twice with ether (2 x 50ml), and the ether extracts dried over sodium sulfate. The solvent is drawn off and the residue distilled. -An effective precision glass stirrer should be used for quantities exceeding 0.1 mol, and the excess of (2) should not be greater than 20%.