Vinyl sulphoxides cycloaddition

For a recent discussion on the stereochemical aspects of the Diels-Alder reaction with vinyl sulphoxides see References 662, 663. It should be pointed out that vinyl sulphoxides can be considered in [2 + 4]-cycloadditions as acetylene synthons since the sulphinyl moiety may be removed from the product by sulphenic acid elimination. Paquette and coworkers took advantage of this fact in the synthesis of properly substituted anthracenes 562664, (equation 360). 

The cycloaddition of nitrile oxides 574 to vinyl sulphoxides usually produces a mixture of regio- and diastereoisomers. Their ratio is dependent on the nitrile oxide used and the configuration around the double bond in the starting sulphoxide (equation 365)673. 

On the other hand, a very high asymmetric induction was observed in the 1,3-dipolar cycloaddition of (/ )-( + )-p-tolyI vinyl sulphoxide 578 with acyclic nitrones. The reaction... 

The use of phenyl vinyl sulphoxide, PhSOCH=CH2, as an acetylene equivalent in Diels-Alder cycloadditions has been developed/ an example being the synthesis of 3,6-diphenylpyridazine (191 Ar = Ph R = H) in 97% yield (Scheme 44 path a). 4-Amino-pyridazines are available also by cycloaddition reactions, in this case between lV-acetyl-4-oxazolin-2-ones, or (better) the unsubstituted oxazolinone, and 1,2,5,6-tetrazines, as illustrated in Scheme 44 (path... 

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