Sulfonyl isocyanates, cycloaddition

Reductive ring opening of the [i-lactam 10 (X = O), obtained by [2 + 2] cycloaddition of chloro-sulfonyl isocyanate and tetraphenylcyclopentadiene followed by treatment with /7-cresol, with sodium hydride in anhydrous tetrahydrofuran yields 3,5,6,7-tetraphenyl-2//-azepin-2-one (11, X = O).41 Surprisingly, similar treatment of the reduced /Mactam 10 (X = H2) is reported to yield 3,5,6,7-letraphenyl-2//-azepine (11, X = H2), the first monocyclic 277-azepine to be isolated and characterized. Physical data for this compound, however, are inconclusive and attempts to reproduce this synthesis have failed.291... 

Some intramolecular [2+2] cycloadditions of sulfonyl isocyanate-olefins have been studied by Metz et al. [116]. These authors found that the intramolecular reaction depicted in Scheme 36 was calculated to be endergonic at the B3LYP/6-31G and B3LYP(PCM)/6-31G levels, the corresponding free activation energies being in the... 

Effenberger, F, Kiefer, G, Stereochemistry of the cycloaddition of sulfonyl isocyanates and A-sulfinylsulfonamides to enol ethers, Angew. Chem. Int. Ed., 6, 951-952, 1967. 

Iminothiazolidines are prepared by the reaction of alkynes with JV,JV -disubstituted thioureas <88SC197>. 2-Oxathiazolidine (363) is formed when the cyclic thione (362) is treated with />-toluen-sulfonyl isocyanate in a [8 + 2]-type cycloaddition reaction (Equation (72)) <92H(34)1415>. 

Sulfonyl isocyanates seem able to undergo stereospecific or highly stereoselective reactions. The cycloadditions of chlorosulphonyl isocyanate to cis and trans isomers of /3-methylstyrene and of 3-hexene were carried with retention of the olefin configuration . The initial products of the following reaction (R = p-MeCgH4S02-)... 

Another case, in which the capture of a dipolar intermediate is reported, is the cycloaddition of an arene-sulfonyl isocyanate to a dialkyl-carbodiimide. One of the ultimate products is a 2 1 adduct, and it is suggested that an open dipolar species, the product of the first addition, adds a second molecule of isocyanate in a subsequent step. Formation of 2 1 adducts is regarded as strong evidence of cycloadditions with polar intermediates . 

Stereochemistry, substituent effects and activation parameters of most ketene reactions are consistent with a one-step cycloaddition polar effects of substituents and solvents, as well as the isotope effect, often require, however, that a fair amount of charge separation (that is, unequal bond formation) characterises the transition state. It has been kinetically proved that cycloadditions of enamines to ketenes can also proceed through a dipolar intermediate this is so for the reaction between dimethylketene and N-isobutenylpyrrolidine . In the latter case, the rate coefficient for the formation of the intermediate strongly depends on solvent polarity itacetonuriie/ cyclohexane = 560. Use of the Same criteria used for ketenes (as far as experimental data allow it) in the case of the 1,2-cycloadditions of fluorinated olefins results, instead, in the conclusion that a two-step biradical mechanism is operating. Results for 1,2-cycloaddition of sulfonyl isocyanates to olefins, cases (g) and (h) in Table 17, give indications of dipolar intermediates during the course of these reactions. 

Chiral vinyl ethers attached to a Wang resin through the p-oxyphenylsulfonyl linker, have been reported to give the [2+2] cycloaddition reaction with chloro-sulfonyl isocyanates (CSI) [226]. The intramolecular alkylation of the (3-lactam nitrogen atom gave mixtures of the corresponding diastereomeric clavams or oxacephams, (Scheme 102). 

Bestian, H., Cycloaddition with Sulfonyl - Isocyanate , Pure Applied Chem.,27,611 (1971). 

In summary, alkyl azides react with aryl isocyanates, acyl isocyanates, carboalkoxy isocyanates and sulfonyl isocyanates to afford the corresponding 1,4-disubstituted A -tetrazohne-5-ones. In contrast, the cycloaddition reaction of aryl azides to isocyanates is hmited to sulfonyl isocyanates, leading to l-aryl-4-sulfonyl-A -tetrazohne-5-ones. 

The reversibility and thermodynamic control of product formation found for the high-pressure reaction between glycals and tosyl isocyanate indicated that the [2+2]cycloaddition of isocyanates to glycals could occur at atmospheric pressure under specific reaction conditions including an excess of isocyanate, as well as proper selection of solvent and substrates. Acyl isocyanates are generally less reactive in [2+2]cycloaddition reactions than sulfonyl isocyanates, except for trichloro- and trifluoroacetyl isocyanate 10,12 addition, acyl isocyanates are problematic because of the competitive formation of [4+2]cycloadducts, which are usually thermodynamically preferred over the [2+2]cycloadducts. 

The cycloaddition to isolated C=C bonds is generally slow, and only highly reactive species, such as sulfonyl isocyanates, react well. The cycloaddition to activated olefins, such as allenes, cyclopentadiene, styrene etc., occurs more readily and many sulfonyl isocyanates and ketenes react at room temperature. The less reactive olefins, such as ethylene, react in the presence of nickel (0) compounds to give five-membered ring metallacycles. Substitution of the olefins by amino or alkoxy groups increases their reactivity in cycloaddition reactions. The approximate order of reactivity is vinyl ethers < enamines < ketene 0,0-acetals < ketene AW-acetals < tetraalkoxyethylene or tetraaminoethylene. 

The substituent R determines the reactivity of the isocyanate. Aromatic isocyanates react faster than aliphatic isocyanates, and carbonyl and sulfonyl isocyanates are considerably more reactive than the former. Isocyanate groups attached to oxygen or nitrogen are not stable in their monomeric forms. In cycloaddition reactions, isocyanates react preferentially across their C=N bonds, but additions across the C=0 bonds are also encountered. In this respect, isocyanates resemble ketenes (see Chapter 4, Section 4.1.). Suitable substrates for cycloaddition reactions are carbon multiple bonds (acetylenes, olefins, ketenes, etc.), C=N bond-containing compounds (imines, amidines, ketenimines, azines, carbodiimldes, etc.), C=0 bonds and C=S bond-containing substrates and phosphorus multiple-bond-containing substrates. Cycloaddition reactions of isocyanates across multiple metal bonds are also known. 

Most [2+2] cycloaddition reactions of isocyanates across the C=0 bond in aldehydes, ketones andlV-substimted amides proceed with elimination of carbon dioxide to give imines 105. The initial cycloadducts cannot be isolated because elimination of carbon dioxide is instantaneous. The reaction of aryl isocyanates with carbonyl compounds requires higher temperatures, while sulfonyl isocyanates react at room temperature ". This reaction can... 

The [2+2] cycloaddition reaction of thioketenes with reactive isocyanates, such as ni-trophenyl or sulfonyl isocyanates, proceeds similarly to give 4-thioxo-2-azetidinones 46". The reactivity of the isocyanates is as follows CISO2NCO > Ph0S02NC0 > 4-MePhS02 NCO > MeS02NC0 > 4-02NPhNC0. 

Azides can undergo cycloaddition reactions with sulfonyl isocyanates as well. L Abbe et al. showed the formation of 4-sulfonyl-tetrazolin-5-ones that underwent thermolylically-induced decomposition and produced carbodiimides with the formation ofNa. ... 

The catalyst-free 5-1-1-cycloaddition reaction between C, A(-cyclic A -acyl azome-thine imines (134) with isocyanides (135) formed imin-l,3,4-oxadiazin-6-one derivatives (136) in high to excellent yields (99%) under mild conditions (Scheme 42). The cobalt-mediated / -pentadienyl (137)/alkyne (138) 5-1-2-cycloaddition reaction yielded /, -cycloheptadienyl complexes (139) under kinetic control. The initial cycloadducts are isomerized to the final >/ -cycloheptadienyl complexes (140) (Scheme 43). The Ru(I)-catalysed intra- and intermolecular 5 4- 2-cycloaddition reactions of 3-acyloxy-l,4-enynes and alkynes produced adducts with highly functionalized seven-membered rings. The reaction sequence includes a 1,2-acyloxy migration. The catalyst-free 5 4- 2-cycloaddition reaction of 2-vinylaziridines with sulfonyl isocyanates in CH2CI2 yielded seven-membered cyclic ureas in high yields (up to 90%). ... 

Sulfonyl imides(RN=S02), generated from alkylsulfamoyl chloride (RNHSOjCl) and triethylamine, react with enamines in the same way as sulfenes do, to give four-membered heterocycloadducts such as 210 Phenyl isocyanate undergoes [2 -t- 2] cycloaddition with enamines affording azetidinones (211) whereas azetidinothiones (212) have been obtained from the reaction of isothiocyanates with enamines without j8-hydrogens . ... 

The [2+2] cycloaddition reaction of isocyanates proceeds better with olefins having electron donating groups attached to the double bond system. Examples include vinyl ethers, enamines, ketene acetals, tetraalkoxy- or tetraalkylaminooleflns. The more reactive sulfonyl and carbonyl isocyanates undergo cycloaddition reactions with vinyl ethers especially well. For example, the reaction of vinyl ethers with p-toluenesulfonyl isocyanate affords the [2+2] cycloadducts in a stereospecific reaction... 

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