Phenyl vinyl sulfoxide route

It was demonstrated that the use of phenyl vinyl sulfoxide or sulfone in a thermal Diels-Alder reaction was highly unsatisfactory as an alternate route. The synthesis of the neolignins galbulin, isogalbulin [82], magnoshinin, and magnosalin [83] have all been accomplished by means of a cation radical cycloaddition (Scheme 42). 

A new route to pyrroles which begins by conjugate addition of p-ketoesters to phenyl vinyl sulfoxide was developed. <94JCS(P1)2355> The adducts are subjected to Pummerer rearrangement which generates 2-phenylthio-dihydrofurans as intermediates. Treatment with amines and HgClj leads to formation of the pyrroles. 

It should be noted that addition of the tributyltin radical to 1-fluoro-1-(phenylsulfonyl)ethene provides phenyl vinyl sulfone as the only isolated product. However, 2-trimethylsilyl-1-fluoro-1-(phenylsulfonyl)ethene reacts with tributyltin hydride in the presence of AIBN to provide (E)-2-trimethylsilyl-1-fluoro-1-tributylvinylstannane. The vinylstannane is an equivalent for the synthon "H2C=CF " providing a convenient route to 2-fluoro-1-alkenes.8 The trimethylsilyl group can be removed with potassium fluoride in dimethyl sulfoxide-water or oxalic acid-methanol at the end of the reaction sequence. 

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