Treatment of ethyl 2-pentynoate (14) with lithium (phenylthio)(tri-n-butylstannyl)cuprate (12) afforded, in 76% yield, ethyl (Z)-3-(tri-n-butylstannyl)-2-pentenoate (15). On the other hand, when compound14was allowed to react with the (tri-n-butylstannyl)copper reagent13, ethyl (E)-3-(tri-n-butylstannyl)-2-pentenoate (21) was produced in 83% yield. Reduction (diisobutylaluminum hydride, ether) of the esters15and21gave the alcohols16and22, respectively. Treatment of each of the latter substances with pyridine – sulfur trioxide complex, followed by further reduction of the resultant intermediates with lithium aluminum hydride, provided the geometrically isomeric alkenylstannanes17and23. Conjugate addition of (E)-3-lithio-2-pentene (18) (formed by transmetalation of17) to compound19produced the olefinic trimethylhydrazide20, which was converted (diisobutylaluminum hydride, ether; pyridinium dichromate, dimethylformamide) into the corresponding carboxylic acid2. Subjection of compound23to a sequence of reactions identical with that used for the conversion of17into2provided the isomeric acid3, which was identical (infrared,1H nmr) with the natural acid derived from triophamine (1). Conversion of3into thep-nitrophenyl ester26, followed by condensation of the latter substance with guanidine, afforded a chromatographically separable mixture of (±)-triophamine (1) and the corresponding diastereomer.