Thiosulfines 3+2 cycloaddition reactions

Thiosulfines, R2C=S=S, are also not stable and rearrangement to thiocarboxyUc esters seems to be faster than reaction with alkynes or norbornadiene. However, numerous [3-1-2] cycloaddition reactions, in which the C=S=S system reacts as a 1,3-dipolar species are known (see Section 2.3.2). 

Alkylidenethioketenes and thioketene 5-ylides (R2C=C=S=CH2) are also described in this chapter. The latter were trapped by an intramolecular cycloaddition reaction to give dithiolanes. Also, propadieneselon, CH2=C=C=Se, is described in this chapter. The unusual extended system, ArN=C=C=C=S, was recently generated by flash vacuum thermolysis ". Thiocarbonyl- -sulfides are treated as Thiosulfines in Section 4.2.2. 

Reactions of cyclopentadienyl- and (pentmethylcyclopentadienyl)iron dicarbonyl 2-alkynyl complexes as well as cyclopentadienylmolybdenum tricarbonyl 2-alkynyl complexes with 4,5-diphenyl-3,6-dihydro-l,2-dithiin 1-oxide 111 were shown to yield transition metal-substituted five-membered ring thiosulfinate esters 112 in moderate to excellent yields (Scheme 27) <19910M2936, 1989JA8268>. These reactions are formal [3-1-2] cycloadditions. When... 

Only a few intramolecular thioaldehyde [4 + 2] cycloadditions have been executed to date. Vedejs et al. have looked at systems such as that shown in equation (88).Their photochemical method is useful in effecting intramolecular reactions but stereoselectivity in the process was only moderate. Baldwin and Lopez have described the single intramolecular cycloaddition shown in equation (89) which involves a new thermal method for generating thioaldehydes from alkyl thiosulfinates. ... 

Other variations of the [3 + 2] cycloaddition chemistry involving either SO2 or a S2O equivalent have been explored (Scheme 47). Iron allenyl complexes undergo reaction with SO2 to give either vinyl iron (105) or (106), depending on the substitution pattern. A propargylic iron complex reacts in a similar manner to give (107), but reacts with a cyclic thiosulfinate ester to give (108). 

H shift. In some cases, e.g., methyl azidoacetate, the sulfur atom extmded in the course of the reaction is intercepted by 1 to give a thiocarbonyl 5-sulfide (thiosulfine, 33), which subsequently undergoes a 1,3-dipolar cycloaddition with 1 yielding... 

Thiocarbonyl S-SulSdes (ThiosulSnes). The formation of the symmetrical 1,2,4-trithiolane (34, eq 14) is the evidence for the intermediacy of thiosulfine 33 formed by a sulfur transfer from thiaziridine 31 to 1. The mixed 1,2,4-trithiolane (51) (eq 22) can result either from the [2 + 3]-cycloaddition of thiobenzophenone 5-sulfide (53) with 1 or from 33 with thiobenzophenone. Both pathways are conceivable for the formation of 51 in a three-component reaction including 1, thiobenzophenone, and phenyl azide. Tetraphenyl-1,2,4-trithiolane (54) undergoes a [2 + 31-cycloreversion and releases 53, which is trapped by 1 to afford 51 (eq 22). The latter is stable under the reaction conditions. ... 

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