Synthesis of thiamono- and thiabicyclanes from sodium sulfide and methanethiolate

Abstract

Keywords: 1-[5-acetyl-3-(methylthiomethyl)tetrahydro-3-thiopyranyl]-1-ethanone, 4-methyl-1-methylthiomethyl-7-thiabicyclo[3.3.1]non-3-en-2-one, sodium methanethiolate, sodium sulfide, condensation.In recent years methods have been developed for obtaining aliphatic and alicyclic γ-keto, γ,γ'-diketo, bissulfides, thiamono-, and thiabicyclanes [1-3] by the alkylthiomethylation of ketones using sodium sulfide and/or thiolate of alkaline sulfide solutions (ASS) from gas or oil refining operations as sulfur-containing reagents.In the present work the four-component condensation of acetone with formaldehyde and sodium sulfide and methanethiolate present in ASS has been studied. The effect of reaction conditions on the composition and yield of the products obtained has been investigated.The condensation of sodium sulfide and methanethiolate of ASS with a twofold excess of formaldehyde and acetone at 20 o C leads after 10 min to 1-[5-acetyl-3-(methylthiomethyl)tetrahydro-3-thiopyranyl]-1-ethanone (1) in 78% yield (on sodium sulfide). The yield of thiamonocyclane 1 grows on increasing the consumption of formaldehyde (Table 1, expt. Nos.1-4) and the content of sodium sulfide in ASS (expt. Nos. 3, 5, 6). An increase in the duration of the reaction aids a reduction in the content of thiamonocyclane 1 due to its conversion into 4-methyl-1-methyl-thiomethyl-7-thiabicyclo[3.3.1]non-3-en-2-one (2), described by us previously in [4], the amount of which in the reaction mixture was 32% after 1 h. Complete conversion of compound 1 into 2 was reached after 13 h at 50-60 o C.The alkylthiomethylation of acetone by formaldehyde and sodium methanethiolate, leading to 5-thiahexan-2-one 3 and 1,1-bis(methylthiomethyl)propan-2-one 4 occurs in addition to the formation of thiamonoand thiabicyclanes 1 and 2. Depending on the concentration of sodium methanethiolate in ASS the yield of γ-keto sulfides 3 and 4 was 3-6 and 32-52% (10 min, 20 o C) respectively. 3-Methylthiomethyl-3-buten-2-one (5) was detected in the reaction mixture with the aid of IR spectroscopy and GLC.