Isoselenocyanates, cycloaddition reactions

Acetamide enters a cycloaddition reaction with thiadiazolium salts 128 in the presence of triethylamine with the formation of heteropentalene stmcture 33, for which an isomerization equilibrium with open form 40 was also proposed (see Section 6.03.4) (Scheme 36) <2003HAC95>. 3-A-Methyl-5-(/>-tolylimino)-l,2,4-thiadiazole hydrochlorides 129 form heteropentalene structures 34 in a cycloaddition reaction with CS2 in nearly quantitative yields (Equation 18) <2003HAC95>. Similar stmctures, including selenium containing products, are obtained by the reaction of compounds 129 with iso-, isothio-, and isoselenocyanates <2003HAC95>. 

Aryl isoselenocyanates 4-RC6H4NCSe (R=H, Br, Cl, MeO) (prepared by selenation and dehydration of A-arylformamides) undergo regioselective cycloaddition reactions with 4-diethylamino-3-butyn-2-one in refluxing THF yielding W-arylselenetimines 11 (Scheme 9) <2004H(62)521>. 

Isoselenocyanates also undergo [2 + 2] cycloaddition reactions across their C=Se bond with carbodiimides to give l,3-selenazetidine-2,4-diimines 228. ... 

The chemistry of isoselenocyanates was reviewed more recently, and their cycloaddition reactions are included in this chapter". ... 

Thiocarbamoyl isoselenocyanates 43 also undergo the [2+2] cycloaddition reaction with imines to give 1,3-selenazetidines 44. ... 

The dithioles 166 undergo a [3+2] cycloaddition reaction with isoselenocyanates to give the dithia-l-selenapentalenes 167. ... 

The synthesis of 1,2,3-selenadiazole derivatives has been reported. The reaction of aroyl chlorides such as 102 with potassium isoselenocyanate and ethyl diazoacetate yielded 5-(aroylimino)-2,5-dihydro-l, 2,3-selenadiazole-4-carboxylate esters such as 104. A reaction mechanism via the initial formation of the corresponding aroyl isoselenocyanate 103 followed by a 1,3-dipolar cycloaddition of the diazo compound with the C=Se bond is proposed <00HCA539>. 

The reactions of isoselenocyanates with carbodiimides in refluxing hexane afford l,3-selenazetidine-2,4-diimines 33 by a [2+2] cycloaddition in moderate to good yields (Scheme 12 and Table 4) <2005HCA766>. These compounds can be purified by silica gel chromatography and recrystallization. All products 33 are stable and can be stored at room temperature. 

In the reaction of 4-chlorobenzoyl isoselenocyanate 139 with diazomethane a regiose-lective [3-1-2] cycloaddition occurs to give the 1,2,3-selenadiazole 140. ... 

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