Conformationally constrained derivatives of 1,3‐dithianes (5‐tert‐butyl‐ and 4,6‐dimethyl‐1,3‐dithiane and dithiadecalin) have been oxidised with various oxidants to yield axial and equatorial sulfoxides, disulfoxides and sulfones. Axial sulfoxides were prepared by nucleophilic hydroxide addition to the corresponding 2‐alkylidene derivatives with subsequent retro‐aldol‐type elimination. The reaction outcome is related to the relative energies of the derivatives, as demontstrated by DFT calculations. The NMR spectroscopic data of the compounds obtained were analysed to identify 4J couplings. It was found that only 4J W couplings can be observed regardless of whether there is an axial or an equatorial sulfoxide, sulfide or sulfone group present in between the respective C–H moieties. A previously postulated γ‐gauche effect of axial sulfoxides (but not of equatorial sulfoxides or sulfones) leading to the shielding of carbon atoms is not unambiguously supported by the NMR spectroscopic data of conformationally fixed derivatives.

Nucleophilic additions of enolates, piperidine and methanol to easily prepared alkylidene[1,3]dithiolane-1,3-dioxides afforded the respective adducts with good yields. Selectivities were strongly dependant from the steric hindrance of the substrate and reached 92:8 to ≥ 98:2 in additions to the phenyl-substituted bissulfoxide product.Alkylidenebissulfoxides 1 have repeatedly been used in organic synthesis due to their electron-deficient double bond. 2 Since unsymmetrically substituted sulfoxides are chiral, these reactions can be led diastereoselectively. Aggarwal and co-workers used very successfully dithianeand dithiolane-derived bissulfoxides of type 2 and 3 in epoxidations, cyclopropanations and cycloadditions ( Figure 1). 3 The cleavage of the auxiliary liberating a carbonyl compound is achieved, for example, by Pummerer reaction. 3b,4 Malacria, Fensterbank et al. used bis(tolylsulfinyl)alkenes of type 1 in Michael-type additions and achieved excellent selectivities in the addition of enolates, cuprates and amines. 5 The stereoselectivities were explained in accordance to an X-ray crystallographic analysis of 1 (R = Ph) showing a p-stacking of the toluene moieties leaving only one side of the molecule free for an attack of the nucleophiles. Recently, we presented dithiane-derived bissulfoxides 2 as acceptors for nucleophilic additions and found high selectivities in the addition of enolates thought steric hindrance (X-ray crystallographic analysis of 2, R = Ph) should be negligible. 6 We think that stereoelectronic effects have a significant influence and should be particularly considered in explanations of selectivities. The method presented by us has been used in an umpoled reaction for the synthesis of 1,4-dicarbonyl compounds.In this letter we wish to report on the utilization of dithiolane-derived substrates 3 as strong Michael-type acceptors.Cycloadditions with the parent methylene[1,3]dithiolane-1,3-dioxide 3a (R = H) have been thoroughly investigated by Aggarwal et al. 3a,b,7 and the methyl derivative 3c (R = Me) has been proposed as an intermediate once. 8 Nevertheless, a synthesis for substituted substrates which were mandatory for our investigations had not been published before our work.We found that the previously used synthetic protocol 6,7 established for the dithiane-derived substrates 2 (Peterson olefination of dithiane and subsequent stereoselective oxidation of the sulfide moieties) is not applicable here. Deprotonation of dithiolane would induce a cycloreversion giving rise to the formation of ethene and dithioformate. 9 Consequently, we tested a method introduced by Okuyama et al. starting with ethane-1,2-dithiol and an acyl chloride. 9 Though yields were in the range of only 33-67%, this method could be used for the convenient and cheap synthesis of ample amounts of alkylidenedithiolanes 4 (Scheme 1). Scheme 1Stereoselective oxidation of the sulfide moieties was achieved by slight modification of the protocol presented previously 6,10 avoiding basic conditions during the workup process ...

Dithiole derivatives R 0175 Alkylidene[1,3]dithiolane-1,3-dioxides as Potent Michael-Type Acceptors. -Asymmetric oxidation of alkylidene dithiolanes provides alkylidene bissulfoxides of type (II) in good yields. They are more reactive towards nucleophiles than the corresponding dithiane-derived analogues. -(WEDEL, T.; PODLECH*, J.; Synlett 2006, 13, 2043-2046; Inst. Org. Chem., Univ. Karlsruhe, D-76131 Karlsruhe, Germany; Eng.) -Mais 50-133