The reactions of sterically crowded cycloalkanethiones of type 2 with CHCl3/NaOH under phase-transfer catalysis (PTC) with benzyl(triethyl)ammonium chloride (TEBA) as catalyst afforded the corresponding 'gem.-dichlorothiiranes' of type 3 in good yields (cf. Scheme 2 and Table). The desulfurization, which, in some cases, occurred spontaneously, led to (dichloromethylidene)cycloalkanes of type 4. Similar results were obtained using Seyferth's reagent in boiling benzene. In the case of 2,2,6,6-tetramethylcyclohexanethione, reaction under PTC conditions after 3 h yielded only the corresponding dichloromethylidene derivative: on the other hand, workup after 1 h gave (2,2,6,6-tetramethylcyclohexylidene)methanethione (thioketene 9; Scheme 5).
Ring expansion and vinylic nucleophilic substitution competing for (tert-alkyl)2CC(Li)–Cl in carbenoid chain processes
(tert-alkyl)2CC(Li)–Cl as transient intermediates. The chains are longer and the overall reactions much slower in tert-butyl methyl ether (t-BuOMe) than in THF as the solvent. In competition with the fast SNV step of these Cl,Li-carbenoids, the Fritsch–Buttenberg–Wiechell (FBW) ringexpansion in t-BuOMe (but less so in THF) generates short-lived cyclohexyne species, which are trapped by the accompanying