The chemistry of 1-phenylseleno-2-(p-toluenesulfonyl)ethyne: Applications towards the total synthesis of virantmycin

Acetylenic sulfones are versatile compounds in synthetic organic chemistry. Among other properties, they can act as electrophiles in conjugate additions or as dienophiles in Diels-Alder reactions. This Dissertation describes the preparation and chemistry of 1-phenylseleno-2-(p-toluenesulfonyl)ethyne.;This novel acetylenic sulfone was prepared from p-toluenesulfonylethyne and benzeneselenenyl chloride in high yield. It reacted with organocopper reagents by syn-addition to give (Z)-1-alkyl-1-phenylseleno-2-(p-toluenesulfonyl)ethenes or (Z)-1-aryl-1-phenylseleno-2-(p-toluenesulfonyl)ethenes. These compounds underwent either selenoxide elimination leading to allenic sulfones or reacted with a second equivalent of organocopper reagent in a stereoselective addition-elimination reaction to form 1,1-dialkyl-2-(p-toluenesulfonyl)ethenes with retention of configuration.;The outcome of addition reactions with heteroatom nucleophiles depended greatly on the particular species used. With the hard alkoxide and amine nucleophiles predominant or exclusive addition at the ;1-Phenylseleno-2-(p-toluenesulfonyl)ethyne was employed as a powerful new diene in Diels-Alder reactions, which typically proceed in high yield under mild conditions, without Lewis acid catalysis. Furthermore, it has been demonstrated that the ensuing products can be further converted into unsymmetrical diaryl selenides or sulfones. The Diels-Alder products can also be converted into cyclic ketones, thus rendering 1-phenylseleno-2-(p-toluenesulfonyl)ethyne as a novel ketene equivalent.;Attempts to isolate the analogous 1-phenylthio-2-(p-toluenesulfonyl)ethyne were unsuccessful. Byproducts from these attempts indicate that this compound can be generated in situ as a highly reactive intermediate that undergoes further conjugate additions under the conditions employed.;The versatility of 1-phenylseleno-2-(p-toluenesulfonyl)ethyne in conjugate additions was further demonstrated by using it as a starting material in a new approach towards the natural antiviral agent virantmycin. The advanced key intermediate methyl (Z)4-(N-carbobenzyloxyamino)-3-...