1985
Scheme 3.
Having developed a new approach to the stereoselective synthesis of 1-sulfinyl-1,3-dienes, in order to
apply this methodology to asymmetric synthesis the preparation of this type of diene in enantiomerically
pure form was required. To this end, applying the same synthetic procedures, but starting with the
readily available optically pure (S)-ethyl p-tolylsulfinylmethylphosphonate13 instead of its racemic form,
the optically pure substrate (E)-4 of (R) configuration at sulfur was prepared (ee>98%, HPLC, Daicel
Chiralpack AS). Heck reaction of (R)-(E)-4 under the usual conditions afforded the 1,3-diene (R)-(E)-
1b14 without any loss of optical purity (ee>99%, HPLC, Daicel Chiralpack AS), proving that there is no
racemization at sulfur under the experimental conditions of the Heck reaction.
In conclusion, we have demonstrated that 1-p-tolylsulfinyl-1,3-dienes 1 can be readily synthesized
in both racemic and optically pure form by formation of the C2–C3 bond via an intramolecular Heck
reaction. The reactivity of the exocyclic dienes 1 in asymmetric Diels–Alder reactions is currently being
investigated in our laboratory.
Acknowledgements
We are grateful to DGICYT (Ministerio de Educación y Cultura, project PB96-0021) for financial
support.
References
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