REACTIONS OF DELTA-VALEROLACTONE WITH LITHIO TRITHIO-ORTHOFORMATES

delta-Valerolactone (3), on treatment with tris(methylthio)methyllithium (7) followed by weakly acidic aqueous work-up, gave a tautomeric mixture of 1,1-bis(methylthio)-6-hydroxy-2-hexanone (8a) and tetrahydro-2-bis(methylthio)methyl-2-pyranol (8b). Under analogous conditions 3 reacted with tris(phenylthio)methyllithium (10) to form tetrahydro-3-(phenylthiocarbonyl)-2-pyranone (11). With 2-(methylthio)-1,3-dithian-2-yllithium (16) it gave a tautomeric mixture of 2-(5-hydroxy-1-oxopentyl)-2-(methylthio)-1,3-dithiane (17a) and 2-(tetrahydro-2-hydroxy-2-pyranyl)-2(methylthio)-1,3-dithiane (17b). Treatment of 17 with methanol in the presence of acidic ion-exchange resin gave a mixture of 2-(5,6-dihydro-3-(methylthio)-2(4H)-pyranyl)-1,3-dithiane (20), 2-(tetrahydro-2-methoxy-2-pyranyl)-1,3-dithiane (21), and 2-(tetrahydro-2-methoxy-4-(methylthio)-2-pyranyl)-1,3-dithiane (22). Similar treatment of 20 gave a mixture of 20, 21, and 22. Compound 21 was synthesized independently by similar treatment of 2-(tetrahydro-2-hydroxy-2-pyranyl)-1,3-dithiane (23). The origins of the anomalous products are discussed briefly. It is concluded that because of these anomalies the preparation of tetrahydro-2-hydroxypyran-2-carboxylic acid acetals and related glycosides via trithio-orthoformate derivatives can encounter difficulties, although dithioacetals may serve this purpose.