Carbene Anion Formation from a Dithioacetal Anion Bearing an Allylic Oxyanion Substituent at the 2 Position. Divergent Behavior of the Dianion in Ether and THF

Article abstract of DOI:10.1021/jo00178a005

The recently proposed principle that diphenyl dithioacetal anions decompose to carbenes when present in a molecule possessing a second anionic site has been applied to a dithioacetal anion possessing an oxyanion at the 2 position.When the alcohol 3, arising from 1,2-addition of tris(phenylthio)methyllithium to crotonaldehyde, is treated with 2 molar equiv of sec-butyllithium at -50 deg C, the dianion 4 is produced by deprotonation and sulfur-lithium exchange.When this dianion is warmed to 0 deg C in THF, the carbene anion that is generated undergoes the expected 1,2-H transfer to yield trans-1-(phenylthio)pent-3-en-2-one (5).The main product (7) of decomposition of the same dianion in ether solution arises by loss of the Li2O and 1,4-addition of sec-butyllithium to the resulting conjugated ketene dithioacetal (10).