Arenesulfonyl isocyanates, reactions with

Commercially important arenesulfonyl isocyanates are not directly accessible from the corresponding sulfonamides via phosgenation due to lack of reactivity or by-product formation at elevated temperatures. A convenient method for their preparation consists of the reaction of alkyl isocyanates with sulfonamides to produce mixed ureas which, upon phosgenation, yield a mixture of alkyl and arenesulfonyl isocyanates. The desired product can be obtained by simple distillation (16). Optionally, the oxalyl chloride route has been employed for the synthesis of arenesulfonyl isocyanate (87). 

Similar [2+2+2] cycloadducts 208 are obtained in the reaction of arenesulfonyl isocyanates with aliphatic carbodiimides... 

Heating of the cycloadducts derived from arenesulfonyl isocyanates with dialkyl-carbodiimides in refluxing o-dichlorobenzene gives rise to the formation of N-sulfonylcarbodiimides and the lower boiling alkyl isocyanate. For example, reaction of p-toluenesulfonyl isocyanate 13 with di-n-butylcarbodiimide affords N-p-toluenesulfonyl-N -n-butylcarbodiimide 14 in 42 % yield. Reactions with DCC and diisopropylcarbodiimide proceed similarly. 

Similarly, alkane- and arenesulfonyl isocyanates gave 2-sulfonyl-2,3-dihydroisoindol-l-ones 11 with benzocyclopropene. 2,3-Dihydroisoindol-l-one was produced as a byproduct in 4% yield in the case of arenesulfonyl isocyanates. Cyclopropa[ ]naphthalene underwent addition to 4-phenyl-47/-l,2,4-triazole-3,5-dione at 20°C almost instantaneously to give an indazole 12 in 92% yield.Both reactions are believed to occur by electrophilic attack on the cyclo-proparene and may involve a zwittcrionic intermediate. When benzyne was generated from benzenediazonium-2-carboxylate in refluxing dioxane in the presence of cyclopropa[Z ]naph-thalenc, 5//-naphtho[2,5-a]indene was formed in 13% yield. 

In contrast, reaction of diazomethane with phenyl carbonyl isocyanate affords an oxa-zolone derivative formed via a [4+2] cycloaddition sequence . Diazomethane reacts with arenesulfonyl isocyanates to give 1,2,3-oxathiazole derivatives. The reaction of phenyl isocyanate with photochemically generated diphenylcarbene gives 2,2-diphenylindoxyl. ... 

Ketene-0,0-, N,N-, N,0-, N,S- and 5,5-acetals react readily with alkyl, aryl and especially arenesulfonyl isocyanates to give 1 1 adducts. The structure of the adducts depends on the degree of substitution on the jS-carbon atom. The /3-disubstituted ketene acetals give [2+2] cycloadducts In the reaction of phenyl isocyanate with ketene diethylacetal, a six-membered ring 2 1 cycloadduct is obtained and mixtures of the [2+2] and the [2+2+2] are obtained from substituted keten 0,0-acetals Heterocyclic e-caprolactim ethers 92, which are in equilibrium with ketene OW-acetals, react with aryl isocyanates at room temperature to give [2+2] cycloadducts 93 and at 150 °C to produce [2+2+2] cycloadducts 94. ... 

The reaction of tropone 107 or 2,7-diphenyltropone with arenesulfonyl isocyanates gives A-sulfonyl imines 108, which react with excess isocyanate to give the bicyclic adducts 109149 ... 

Across C=N bonds The cycloaddition reactions of isocyanates across C=N bonds usually afford [2-1-2] and [2-I-2-I-2] adducts but linear 1 1 adducts are also encountered. If the reaction is concerted, as in the dimerization of isocyanates, the four-membered ring [2-1-2] cycloadducts are obtained. However, when the reaction proceeds stepwise, the initial acyclic polar adduct can be intercepted by either the isocyanate or the substrate to give [2-I-2-I-2] cycloadducts. If the lifetime of the initial acyclic adduct is shorter than the time for rotation around the bond formed, the process is indistinguishable from the concerted reaction . An exchange reaction may proceed via the intramolecular [2-1-2] cycloaddition and the new set of double bonded substrates and heterocumulenes can participate in the reactions. An example is the cycloaddition reaction of arenesulfonyl isocyanates with carbodiimides. ... 

Two equivalents of the isocyanate react with cyanotrimethylsilane at 50 °C to give a flve-membered ring [2+2+1] cycloadduct. Af,Af -disubstituted 5-trimethyl-silyliminoimidazolidinediones are obtained in the reaction of aryl- or arenesulfonyl isocyanates with trimethylsilyl cyanide. In the reaction with arenesulfonyl isocyanates the initially formed insertion products can also be isolated. The reaction of trimethylsilylamldes with phenylcarbonyl isocyanate also affords the insertion product. 

The polar cycloaddition reaction of arenesulfonyl isocyanates with carbodiimides gives rise to the formation of cyclic six-membered ring 2 1 adducts 56 and 57 . N-Sulfonylcarbodiimide is generated in an exchange reaction as shown in the following reaction scheme. 

The reactions of metal substituted carbodiimides 20 with arenesulfonyl chlorides or arene-sulfonyl isocyanates produce metal substituted N-sulfonylcarbodiimides 21 (R3M=Me3Si, Et3Ge, Bu3Sn X=C1, NCO). ... 

The reactivity of isocyanates in [2+2] cycloaddition reactions is as follows alkyl < aryl < nitroaryl << arenesulfonyl < halosulfonyl. Also, the reactivity of the substrate is determined by the substituents. For example, vinyl ethers and enamines are more reactive than olefins. Often the formation of the [2+2] cycloadducts involves polar linear intermediates, which can be intercepted by the isocyanate or the substrate to form six-membered ring [2+2+2] cycloadducts (see Section 3.3.1.4). Also, diynes react with isocyanates to give six-membered ring [2+2+2] cycloadducts. In the latter reactions catalysts play an important role. From Q, ty-diynes macrocyclic adducts are obtained. 

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