Sulphines cycloaddition

I. Cycloaddition of Sulphur Monoxide and Sulphines to Unsaturated Compounds... 

Due to the presence of a heterocumulene unit, sulphines may be considered as a group of compounds which are able to undergo cycloaddition reactions. Reaction of sulphines with enamines and phosphorus ylides reported by Sheppard217 and Trippett218 and their coworkers may be considered formally as an example of [2 + 2] cycloaddition. In fact, Sheppard and Dickman217 obtained a 1 1 adduct from thiofluorenone S-oxide and 1-morpholinocyclohexene to which they assigned the dipolar sulphoxide structure 168. 

The [4 + 2] cycloaddition of a-phenylselenopropenoyl trimethylsilane (75) with 2,3-dimethylbuta-1,3-diene is unusual in that a significant portion of product mixture consists of the hetero-Diels-Alder dihydropyran adduct 76. The phenylselenenyl substituent appears to be responsible for this unusual pattern of reactivity, since propenoyl trimethylsilane gives only the expected regioisomer (77, X = H) (Scheme 116)14. a-Selenenyl substituted a,/l-unsaturated acyl silanes such as 75 were used to prepare a series of substituted dienes in excellent yields through the addition of a-sulphinyl carbanions, Brook rearrangement and expulsion of sulphinate, in a reaction pathway recognisably more typical of acyl silanes (Scheme 117). 

One special case is that of the reactive intermediates, the sulphenes (252), and the isolable compounds, the sulphines (253). In the first place, cycloadditions of these species... 

The Strategy above suffered from a lack of regiocontrol in the cycloaddition step. A modification [113] used vinyl sulphones 222 which reacted regio-selectively with pyrazolidinium ylide 218 to give the cycloadducts 223 (Scheme 64). Base-catalysed elimination of benzene sulphinic acid led to the desired bicyclic pyrazolidinones 220a to d. These compounds could also be prepared without racemisation from the optically pure pyrazolidinone 216, derived from L-serine [114]. 

The cycloaddition reaction of sulphines with 1,3-dienes, yielding six-membered ring sulphoxides (117), has been investigated in some detail. ... 

Dienes undergo [4 + 2]cycloaddition with sulphines. The reaction is exemplified by synthesis of (125), which is so unstable that isolation of the sulphone (126) is preferred. A study of the base-catalysed exchange of protons a to the sulphoxide group in (127) and (128) showed that in (127) the endo- roXon was more easily removed but in (128) the exo-proton exchanged... 

Reactions.—Condensation of thiet sulphone with 2 moles of halogeno-hydrazones, RC(Cl)=NNHPh, gives isoimidazoles (113). Cycloaddition of thiet sulphone to cyclopentadiene occurs with an exofendo ratio of 0.25. 2,4-Diphenylthiet dioxide is hydrolysed to dibenzyl sulphone with base, but rearranges to the isomeric sulphinate 3,5-diphenyl-1,2-oxathiolen 2-oxide with concentrated sulphuric acid. Treatment of 4-phenyl-2i/-thiet 1,1-dioxide with KOH in ethanol gives 3-ethoxy-2-phenylthietan 1,1 -dioxide. ... 

A further report on a [ r -1- tttt]-cycloaddition of a diene and SO2 has appeared " the reaction of o-quinodimethane with SOj afforded mainly the cyclic sulphinate (182), and only small amounts of the [n -1- nn] product were formed. 

Four-membered Rings.—Open-chain sulphinate esters are readily prepared but their cyclic analogues are less easily come by. [2 + 2]Cycloadditions involving SO2 are limited to a few specialized examples, and it has been suggested that it is this mode of reaction that leads to the initially formed adduct (274) between SO2 and ketenimines. These compounds are unstable and rearrange to thiazetidine 5-oxides (275) in 90% yield. A versatile approach has been... 

The first stable 1,2-dithietan has also been isolated. The sulphoxide (200), which is the onion lachrymatory factor, has been shown to dimerize when kept in benzene for 7 days in the absence of light, to the rra/w-dithietan (201). This has been rationalized as a [4 -f 2]cycloaddition in which the sulphine functions as a dipole and as a dipolarophile. 

Thermolysis of the dimer (243) leads to the formation of the relatively inaccessible thioketone S -oxides (sulphines) (244), and the cycloaddition reactions of... 

Tetra(phenylthio)ethylene is formed to the extent of 30% during retro-cycloaddition of the sulphine-dimethyldiazomethane cycloadduct (48) by dimerization of the corresponding carbene/"... 

The reaction of sulphines with diazoalkanes or aryl-substituted diazomethanes has been studied by several groups of workers. Although the reaction course was found to depend on the nature of the reactants, the rather comprehensive experimental material available seems to reflect clearly that the normal reaction of sulphines with diazoalkanes is a cycloaddition reaction leading to the formation of A -l,3,4-thiadiazoline 1-oxides (177). " The observation that different products were obtained by the action of 2-diazopropane on different geometrical isomers of the... 

A -l,3,4-Thiadiazolines.—The cycloaddition of aromatic sulphines to nitril imines is a regiospecific non-stereospecific reaction resulting in the formation of A -l,3,4-thiadiazoline derivatives. Interaction of the sulphines (137) and diphenylnitrilimine [generated in situ by the action of triethylamine on N-a-chlorobenzylidene-N -phenylhydrazine (138) in boiling benzene] gave uniform 1 1 adducts that were identified as the A -l,3,4-thiadiazoline S-oxides (139), the alternative 1,2,3-thiadiazoline structure (141) being conclusively eliminated on the basis of chemical and spectroscopic evidence. The non-stereo specific nature of the reaction was demonstrated and its significance discussed. ... 

The cycloaddition of 2-diazoalkanes to aromatic sulphines (thione S-ox-ides), readily accessible by peroxy-acid oxidation of thienes, provides yet another efficient route to A -l,3,4-thiadiazolines (156). Thiobenzophenone S-oxide (155) and 2-diazopropane, for example, afford 2,2-dimethyl-5,5-di-phenyl-1,3,4-thiadiazoline 1-oxide (156). Photolysis to the azines (157) and (158) establishes the orientation of the cycloaddition, and excludes the alternative formulation (159)." Thiofluorenone S-oxide (160) similarly yields spiro-compounds of type (161). " ... 

The steric course of this cycloaddition has been studied" by an examination of the interaction of 2-diazopropane with the geometrical isomers of sulphines in ether at -20 °C. In all examples, each of the geometrical isomers yields a single distinct product. The sum of the observations shows that the spatial arrangement of the S=0 group and the substituents R and R is retained in the product. The cycloaddition is therefore a stereospecific process, involving most probably a concerted process in the formation of product. The presence of bulky substituents in either of the reactants sterically hinders the cycloaddition to the five-membered ring-system, and favours alternative reaction paths, of which the... 

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