Sulfines and Related Compounds

Sulfines, which are thiocarbonyl mono-5-oxides, represent another type of reactive 0=S heterodienophile. This functional group is nonlinear and can exist as (Z)-21 or (E)-22 isomers which have good configura- 

In recent studies, Zwanenburg and co-workers looked at reactions of several sulfines bearing chiral auxiliaries.(Z)-Sulfine 23 prepared from camphor was found to undergo totally stereospecific Diels-Alder cycloaddition with 2,3-dimethylbutadiene giving only one diastereomeric product [Eq. (19)]. 

It was assumed that cycloaddition occurs via the sulfine conformation shown in 23 and that the diene approaches from the least congested Cs,Sre face, giving the observed adduct stereochemistry. It was also found that the relative stereochemistry between chlorine and the sulfur bearing oxygen is retained (syn) in the product. 

Another type of chiral sulfine 24 was prepared from an optically active 

Cydization of either the A -methyl or N-tosyl sulfine with 2,3-dimethylbu-tadiene gave a single diastereomeric adduct, assumed to have structure 25. 

---

Thiocarbonyl oxides are a subject of active investigation. The natural occurrence of sulfines and related compounds in plants of the genus Allium (onion, garlic, etc.) is included in a superb and extensive review by Block [91]. Two detailed papers [92, 93] report the isolation of zwiebelanes from onions and their chemical synthesis involving intermediate sulfines produced by oxidation of di-l-propenyl disulfide, subsequent sulfoxide accelerated [3.3] sigmatropic shift and the [2+2] cycloaddition of the C=S and C=S=0 moieties. A further article [94] provides a great deal of information on the mechanism of formation of (Z)-propanethial S-oxide, the lachrymatory factor of the onion, as well as its chemical synthesis and reactions. Techniques of analysis of the volatiles of onions have been further improved [95]. 

The studies discussed earlier in this chapter focused on the photophysics of met-allo-l,2-enedithiolates and possible applications for these complexes. In addition to being emissive, several (diimine)Pt(dithiolate) complexes photochemically activate molecular oxygen. Recent reports by Srivastava and co-wwkers showed that (bpy)Pt(tdt) and related compounds are sensitizers for the formation of singlet oxygen [81 -83], the generation of which leads to decompositirai of the parent metal complex. The end-products from these reactions are similar to those obtained from the thermal and photochemical oxidation of Ni(II) and Pd(II) dithio-lates [84-87]. These reactions give stable metal-sulfinate (M[SQ2R]) and metal-sulfenate (M[SOR]) derivatives. Collectively, this work parallels the photo- and thermal oxidation of thioethers (RSRO [88-90]. 

The chemical reactivity of the cumulenes under discussion ranges from highly reactive species to almost inert compounds. While some cumulenes can only be generated in a matrix at low temperatures, others are indefinitely stable at room temperature. For example, sulfines and sulfenes are only generated in situ, but some cumulenes with bulky substituents are sometimes isolated at room temperature for example, C=C=S was detected in interstellar space by microwave spectroscopy, and its spectrum was later verified by matrix isolation spectroscopy. In contrast, some cumulenes, such as carbon dioxide and carbon disulfide, are often used as solvents in organic reactions or in the extraction of natural products. The reactivity of some center carbon heterocumulenes in nucleophilic reactions is as follows isocyanates > ketenes > carbodiimides > isothiocyanates. However these reactivities do not relate to the reactivities in cycloaddition reactions. Often reactive cumulenes are isolated as their cyclodimers. Aromatic diisocyanates are more reactive than aliphatic diisocyanates in nucleophilic as well as cycloaddition reactions. 

In a second type of sulfur compounds, sulfur is found usurping the place of carbon for example, related in structure to the ketones are the sulfoxides and sulfones, and related in structure to the carboxj l group are the sulfinic acids. Since sulfur ma> possess a variable valence, it maj give rise also to sulfonic acids which Ix ar the same relation to the sulfinic acids that sulfuric does to... 

Both cis- and rrans-l-arylsulfonyl-2-arylsulfenyl propenes (56) underwent a Smiles rearrangement under electron impact at 20 and 70 eV and formed a diarylsulfide ion [M — 104]+ (equation 27a)39 through a process where a bond between the R C H group and the sulfide sulfur is formed and a rearomatization occurs by a loss of the neutral thiirene dioxide or a simultaneous expulsion of SOz and propyne. The ion m/z 148 was also obtained from all of the sulfonyl-sulfides, 56 (equation 27b) and here the loss of R2 seemed to be related to the bond strength39. In addition to the above compounds 56 exhibited some simple cleavages before and after sulfone-sulfinate rearrangements. 

The related t rt-butylsulfinyl compound 432 may also be converted, by a different mechanism, to the thioxopenam 290b (PPh3, refluxing CH2CI2). Intermediates of this reaction are the sulfinic acid 433 (which could be trapped by diazomethane) and its triphenylphosphine addition product, representable as the penta-coordinate phosphorous species 434 [160]. 

---