N-Sulfinyl compounds

Usually, N-sulfinyl compounds (59) behave as thionyl transfer reagents, similar to, but milder than, thionyl chloride. For example, o-diamines with A-sulfinylbenzeneamine (59 R = Ph) afford fused 1,2,5-thiadiazoles, as in Scheme 8a.77 The advantage of using Af-sulfinyl compounds, rather than thionyl chloride itself, is that concomitant chlorinations and oxidations are avoided. This is of particular importance in the synthesis of 2,1-benzisothia-zoles (Section V,B,6). Singerman s reagent, N-sulfinylmethanesulfonamide (60) is especially valuable 78 it was used very successfully in the synthesis of a series of benzobis(isothiazoles).79... 

There have been some reports of the use of N-sulfinyl compounds to transfer both a nitrogen and a sulfur atom. An example is the reaction of N-sulfinylcyclohexylamine (59 R = cyclohexyl) with diphenylcyclopropenone in the presence of nickel tetracarbonyl. An isothiazolinone S-oxide (62) was the product.80 Similarly, A-sulfinyl-/>-toluenesulfonamide (59 R = tosyl) and the Wittig reagent triphenylphosphonium phenylbenzoylmethylide give 1,2,3-thiadiazoline (63).8 ... 

As noted above, the stereochemical outcome at sulfur in these cycloadditions is not yet understood. Relatively few systems, particularly among the older examples, have been well characterized with respect to sulfur stereochemistry and thus existing data are sparse. Moreover, although N-sulfinyl compounds prefer to exist as the (Z)-isomers, it is not clear if they always undergo cycloaddition in this geometrical form. It is also known that the Diels-Alder reactions of N-sulfinyl compounds are sometimes reversible, which complicates the issue. ... 

The reaction probably involves an initial [2+2]-cycloaddition of the aldehyde and the N-sulfinyl compound to produce an adduct 2 [10] which loses sulfur dioxide to yield the N-sulfonyl imine. Isolated yields of the sulfonyl imines shown in Scheme 1 were generally quite good. In the case of the enolizable aldehyde dichloroacetaldehyde, only a low yield of N-sulfonyl imine was produced. An attempt was also made using these same reaction conditions to convert butyraldehyde to the corresponding Af-tosyl imine [6]. However, all that could be isolated here was the bis-sulfonamido acetal. 

Thus, the most stable configuration of N-sulfinyl compounds is apparently (Z)-3 and for sulfur diimides, ( ,Z)-7 or -8. Interactions within a specific molecule can alter the relative stability of the isomeric forms so that in solution configurational equilibria may exist. 

As stated in the Introduction, N-sulfinyl compounds bearing electron-withdrawing substituents react as heterodienophiles. Arylsulfinyl derivatives usually require heating for a reaction to occur, whereas other types of N-sulfinyl dienophiles will often cycloadd near room temperature or below. In fact, these cycloadditions are sometimes dangerously exothermic when run in the absence of a solvent, and usually an inert solvent such as benzene, toluene, or cyclohexane is used.2 ... 

Sulfur diimides and iV-suIfinyl compounds have nonlinear structures and are configurationally stable at room temperature. Two geometric isomers are possible for N-sulfinyl compounds [i.e., (Z)-3 and (0-4]. Sulfur... 

Dihydrothiazine oxide 15 was proposed to result from initial addition of the electrophilic sulfur atom of the N-sulfinyl compound to ( ,Z)-diene 11 to form a dipolar intermediate [Eq. (11)]. 

Based on these results, Hanson and Stockbum proposed that other dienophiles of electrophilicity comparable to that of iV-sulfinylethyl carbamate (i.e., iV-sulfinylsulfonamides) cycloadd via a similar pericyclic mechanism. They suggested that the observations of Mock and Nugent" could be best explained by a concerted mechanism for the cycloaddition of N-sulfinylsulfanamides 9 to dienes 10 and 11 and a nonconcerted, two-step mechanism for the cycloaddition of 9 to the highly hindered (Z,Z)-diene 12. These workers have proposed that less electrophilic dienophiles, such as N-sulfinylanilines, also undergo cycloaddition via a concerted process. Such concerted [4 -I- 2] cycloadditions for N-sulfinyl compounds are in accord with orbital symmetry considerations."... 

Weinreb N-Sulfinyl compounds as heterodlenophlles [84JACS7861,84JOC3243, 85TET1173]... 

Reactions with N-sulfinyl compounds. — S-(Sulfonylamino)-sulfinyloxypyridinium betaines from N-thionylsulfonamides. Pyridine N-oxide added to a soln. of N-sulfinylbenzenesulfonamide in abs. benzene l-(benzene-sulfonylaminosulfinyloxy)pyridi-nium betaine. Y 92%. 

Kresze G, Wucherpfennig W. Reactions with N-sulfinyl-compounds. 8. Formation and fragmentation of N-aryl-sulfonyl-imide chlorides. Chem. Ber. Rec. 1968 101(1) 365-370. 

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