Thiolane basicities

The order of decreasing Lewis basicity toward trimethylaluminum is thiane, thiolane, diethyl (or dimethyl) sulfide, thietane and 2-methylthiirane (67IC1461). Thietane can be protonated at -60 °C with fluorosulfonic acid in antimony pentafluoride-liquid sulfur dioxide the NMR spectrum shows bands at 8 7.40 (S—H) and 3.20-4.40 p.p.m. (C—H) (71JOC1121). 

These show marked similarities to their acyclic counterparts, e.g. tetrahydrofuran closely resembles diethyl ether. Minor differences arise due to the less sterically hindered nature of the heteroatoms in the cyclic compounds. The basicities are tetrahydropyrrole (pKa 10.4), tetrahydrofuran (— 2.1) and tetrahydrothiophene (thiolane) ( — 4.5). 

The basicity of the sulfoxide oxygen has been investigated by observing infrared shifts in protic solvents. ° In this way, it was shown that thietane 1-oxide is more basic than cyclobutanone, but less basic than tetramethylene sulfoxide (thiolane 1-oxide) or pentamethylene sulfoxide (thiane l-oxide). ° Toward phenol, the order of basicity is as follows thiolane 1 -oxide > diethyl sulfoxide > thiepan 1-oxide > dimethyl sulfoxide > thiane 1-oxide > 9-thiabicyclo[3.3.1]nonane 9-oxide > 7-thiabicyclo[2.2.1]heptane 7-oxide > thietane 1-oxide.ThepKaof the conjugate acid of thietane 1-oxide is — 1.92, as determined in aqueous sulfuric acid. =... 

Thian and thiolan S -oxides have a similar basicity in dilute aqueous solutions, but thietan S -oxide is a somewhat weaker base. The axial SO bond of... 

A series of reports by Russian authors have appeared, dealing with the reaction of esters and ethers of 3-hydroxysulpholen and its 3-arylamino- and 3,4-epoxy-analogues under basic conditions. Isomerization reactions of sulpholens have been studied. The reaction of the 3-keto-thiolan (70) with 0CH(CH2)3C02Me in pyridine, followed by reduction with NaBHi (Scheme 3), gave (70a), a compound of potential value in the synthesis of biotin. ... 

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