A Novel Synthesis of 1,4-Dicarbonyl Compounds via Stabilized Sulfur Carbanions generated by Thiophilic Addition to Sulfines

Patrick Metzner* and Catherine Leriverend

Laboratoire de Chimie Moleculaire et Thio-organique, ISMRA-Universite,

6 Boulevard du Marechal Juin, 14050 Caen, France

The sulfines 2 (thiocarbonyl oxides) are easily available by oxidation of trithiocarbonates 1 with one equivalent of a peroxycarboxylic acid (mCPBA). These stable compounds 2 bear an electron deficient sulfur atom, which can allow the attack of a nucleophile to take place on the sulfur atom rather than the classical mode on carbon of molecules bearing a C=X moiety (X=O, N...).

We were pleased to observe that addition of one equivalent of methyllithium to sulfines 2 at -78°C produced the stabilized anions 3, arising from selective thiophilic addition. Subsequent reaction of 3 with enones 4 occurred only in a conjugate fashion leading to adducts 5. Steric decompression around the sulfur substituted carbon occurred spontaneously via elimination of methanesulfenic acid to afford [[beta]]-oxoketenedithioacetals 6. Synthetic routes to these unconjugated moieties are scarce compared to the straightforward [[alpha]]-oxoketenedithioacetals.

Further transformation can be achieved by an easy "hydrolysis" of ketenedithioacetal moiety to give the thiolester group. Thus we obtained 4-oxothiolesters 7 in good yields. These arise from the formal 1,4-addition of an alkylthiocarbonyl anion synthon to Michael acceptors. It should be noted that, in contrast to the now classical "Umpolung" reagents, the intermediate anions were prepared by addition and not by deprotonation, thus allowing further perspectives for use with multifunctional compounds.

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