Methoxyalkenes

The addition of phenyl tellurium tribromide to internal alkenes in methanol as solvent gives vic-methoxyalkyl phenyl tellurium dibromides. Treatment of these dibromides with 0.5 M aqueous sodium hydroxide solution produces a-methoxyalkenes via an intermediate alkyl phenyl tellurium oxide2,3. The same reaction sequence but starting with terminal olefins3 or cyclohexene2 leads to 2-methoxy-l-alkyl phenyl tellurium oxides, which decompose only at 250° in a vacuum. 

Addition of phenyl tellurium tribromide to terminal olefins in methanol as the reaction medium, yields 2-methoxyalkyl phenyl tellurium dibromide. Hydrolysis of the dibromides with sodium hydroxide in aqueous THF produces 2-methoxyalkyl phenyl tellurium oxides, which, upon heating at 240°, form 2-methoxyalkenes . ... 

A similar reaction carried out with cyclohexene led to the formation of 3-methoxycyclohexene When this reaction sequence is carried out with internal olefins, the methoxyalkyl phenyl tellurium oxides are not stable and decompose to methoxyalkenes in the basic medium required for the hydrolysis of the methoxyalkyl phenyl tellurium dibromides(see p. 583). Aqueous solutions of sodium hydrogen carbonate cause the same transformations at a slower rate". Thus, 5-hydroxy and 5-methoxy-4-hexyl phenyl tellurium dibromide were converted to the corresponding 5-substituted 3-hexenes. 3-Hydroxy- and 3-methoxy-l-cycloheptene were similarly obtained. ... 

Methoxyalkenes (45), derived from IV-Boc or N-Cbz a-amino acids, undergo stereoselective addition of PhSeCl in the presence of (Pr 0)4Ti and LiCl to give the corresponding phenylselenenyl aldehydes (46) that can be easily transformed into enantiomerically pure aziridines (47) on reaction with peroxy acids. 

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