Thiopyran 1,1-dioxides, tetrahydro

Further 4//-thiopyrans as well as 2//-analogs were reduced mainly to their corresponding tetrahydro derivatives. In addition, the hydrogenation of 4//-thiopyran-5,5-dioxides have been described. 

Tetrahydro-4H-thiopyran-4-one [ 1072-72-6] M 116.2, m 60-62 , 61-62 , 64-65 , 65-67 . Purified by recrystn from diisopropyl ether or pet ether and dried in air. If too impure then dissolve in Et2O, wash with aq NaHCO3, then H2O, dried (MgSO4), filtd, evapd and the residue recrystd as before. [Cardwell JCS 715 7949], The oxime can be recrystd from CHCl3-pet ether (at -20°) and has m 84-85° [Barkenbus et al. JOC 20 871 7955]. The 2,4-dinitrophenylhydrazone has m 186° (from EtOAc) [Barkenbus et al. JOC 16 232 7957]. The S-dioxide is recrystd from AcOH, m 173-174° [Fehnel and Carmack JACS 70 1813 7945]. 

Dihydrothiopyran dioxide 284 disproportionates to a mixture of 2H-thiopyran 285 and its tetrahydro derivative 286 in the presence of piperidine,300 as shown in Eq. (14). 

Sulfones derived from tetrahydrothiopyran-4-ones are dehydrogenated to the corresponding thiopyran-4-one 1,1-dioxides by treatment with I2 in DMSO-H2SC>4 the reaction is particularly efficient when aryl groups, with the exception of furyl, are present at the 2- and 6-positions (Equation 93). For the formation of 4//-thiopyran 1,1-dioxide from the tetrahydro precursor a higher yielding three-step sequence (Scheme 100) is preferred <1995JOC1665>. 

The application of 111 NMR spectroscopy to probe both conformation and stereoelectronic effects in tetrahydro-277-thiopyrans and the 1-oxides and 1,1-dioxides continues <2007CEJ4273, 2007MRC590>. 

Allylation of Tetrahydro-2-phenylselenyl-2//-thiopyran 1-Oxides and 1,1-Dioxides General Procedure13 ... 

A solution of 2.0 mmol of the tetrahydro-2-phenylselenyl-2W-thiopyran 1-oxide or 1,1-dioxide, 830 mg (2.5 mmol) of tributyl(2-propenyl)tin and 20 mg of A1BN in 5 mL of C6H6 is refluxed under N2. 20 mg of AIBN is added every 5 h to the reaction mixture until the starting material has completely disappeared (TLC). The solvent is evaporated and the residue filtered (silica gel. fctOAc/pctrolcum ether 1 5, then EtOAc, CH,OH 20 1) lo give the crude product, which is analyzed by spectroscopic methods to determine Ihe product distribution. For analytical purposes, the products are purified by flash chromatography or recryslalli/ed. 

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