Thiopyranone

Ketene dithioacetal 82 reacts with aromatic methyl ketones to generate thiopyranones. Further reaction with ethyl mercaptoacetate leads to the formation of thieno[3,2-f]pyranones in good yields (Scheme 18) <1997BML3101>. 

Thiopyranones containing an alkyne group, upon treatment with OT-chloroperbenzoic acid (MCPBA), undergo a sulfoxide rearrangement to afford thieno[3,2-f]pyrans (Equation 63). In some cases, where the aryl group is substituted with a chlorine atom in the 2-position, or disubstituted with chlorine atoms in both 2- and 4-positions, oxidized products, 130, were formed <2002T10309>. 

Ring expansion reactions are much better known and sulfolene substrates have received considerable investigation. Cyclopropanation with dichlorocarbene affords 6,6-dichloro-3-thiabicyclo[3.1.0]hexane 3,3-dioxides which may readily be ring enlarged by base or acid treatment. Base treatment, especially with LDA, cleanly affords 2//-thiopyran dioxides hydrochloric acid does likewise, but less cleanly, while hydrobromic acid treatment causes a more complex set of reactions leading to thiopyranones containing bromine in which the sulfur has been reduced. The intermediacy of thiopyrylium oxides has been invoked to rationalize the observations (Scheme 27) (81JOC4502). 

This method has been used to prepare the 3-oxidothiopyrylium betaine (42) as its perchlorate salt by oxidation of thiopyranones (75JCS(Pl)2099) with trityl perchlorate (equation 114). 

The reaction of arylidenecyclonones with hydrazines proceeds with the formation of regio- and stereoisomers. Thus, treatment of bisbenzylidene-4-thiopyranones 66 with propylhydrazine 67 in boiling methanol yields mixtures of two isomeric pyrazolines 68 and 69, with 68 predominating [90] (Scheme 2.17). The amount of isomer 69 increases when X is S to SO and S02. 

Direct intermolecular aldol reactions, catalysed by proline, between tetrahydro-4H-thiopyranone (25) and racemic aldehydes exhibit enantiotopic group selectivity and dynamic kinetic resolution, with ee% of >98% in some cases.109... 

There have been relatively few examples of fully assigned 13C NMR spectra of thiopyranones over the last ten years selected data for some substituted thiopyran 2- and 4-ones and related thiones have been assigned (Figure 43) <1976CJC280>. 

There have been extensive 13C NMR data reported for benzo-fused thiopyranones (Figure 44) <1976CJC280, 1983SAA693, 1998PS(134)295>. 

Figure 50 Infrared stretching bands for some thiopyranones and their benzologues.

A selection of methods which have been used to convert thiopyrans and related compounds to their 1-oxides or 1,1-dioxides is presented in Table 28 and reagents used to oxidize various thiopyranone derivatives at sulfur are collated in Table 29. 

Two sequential thio-Claisen condensations convert dialkyl ketones into thiopyran-4-ones in a rapid, high-yielding process. Initial reaction with an aromatic dithioester produces an a, 3-unsaturated ketone which, after alkylation at sulfur, undergoes reaction with a second dithioester and cyclization to the substituted thiopyranone follows (Scheme 200) <1993JOC3042>. 

At 638 nm in cyclohexane, the wavelength of maximum absorbance of the bis(naphtho[l,8-A ]thiopyranone) 628 is 98 nm to the red of thioindigo (Amax 540 nm). These values are in close agreement with those predicted by a TD-PBE0/6-311+G(2, />)//PBE0/6-311G6f,/>) approach that allowed for bulk solvent effects by means of a polarizable continuum model <2006JA2072>. 

Reaction of tetrahydro-4/7-thiopyranone 795 with meso-794 gave the bridged oxathiocins 775 in 68% yield and 92% ee, respectively. Oxazocine 775 existed exclusively in the hemiacetal form, suggesting that the stereocenter originating from C-6 in 794 could be set under thermodynamic control. Reaction of 795 with the readly available 3.5 1 mixture of ( )-794 and meso-794, respectively, produced 775 in the same yield and ee. 

Chalcogenopyranones are weak nucleophiles that can be alkylated to the oxygen atom by powerful alkylating agents thus thiopyranones 140... 

Thiopyranthiones behave similarly to thiopyranones they can be protonated or alkylated to the exocyclic sulfur to give mercaptothiopyrylium salts [75MI2 84ZN(A)267] or alkylthiothiopyrylium salts, respectively. 

---