Isocyanates carbodiimides

Other six-membered rings with two heteroatoms are also obtained from reaction of diketene with imidates, cyanamides, carbodiimides, isocyanates, oxa2olines, or other multiftmctional compounds. 

As representative examples for the reactivity of the Cp Ti(amidinate) complexes some reactions with CS2 and COS are shown in Scheme 88. Other reagents that have been investigated in this study include carbodiimides, isocyanates, CO2, PhNO as well as aldehydes, ketones, and imines. ... 

In contrast to 4-alkyl-5-sulfonylimino-A -l,2,3,4-thiatriazolines (58) (Section 4.19.5.1.2), 4-alkyl-5-alkylimino-A -l,2,3,4-thiatriazolines (50) react with immediate nitrogen evolution when added to electron-rich alkenes or to heterocumulenes such as enamines, carbodiimides, isocyanates, isothiocyanates, or styrene. Reaction kinetics for certain of this type of system show that they undergo bimolecular processes as described below. 

Carbon-13 shifts of azacumulenes, including ketenimines, diazoalkanes, carbodiimides, isocyanates and isothiocyanates, can be readily interpreted in terms of mesomeric effects described by cannonical formulae. 

Review. New synthetic reactions based on the onium salts of aza-arenes have been reviewed (75 references). The reactions discussed involve activation of carboxylic acids or alcohols with 2-haIopyridinium, benzoxazolium, benzothiazolium, and pyridinium salts to afford 2-acyloxy or 2-alkoxy intermediates, which can be transformed into esters, amides, thiol esters, (macrocyclic) lactones, acid fluorides, olefins, allenes, carbodiimides, isocyanates, isothiocyanates, and nitriles under appropriate conditions. 

The syntheses from [2+3] atom fragments are neither as general nor as important as those from [1+4] atom fragments. Wrackmeyer et at. have found thatm-2-boryl-l-stannylalkene 195 reacts with carbodiimides, isocyanates, and isothiocyanates as shown in Scheme 24 <2001CHE1396>. The reaction of 9-cyclopentyl-9-borabarbarlane 196 with acetone takes place with rearrangement to cyclooctatriene derivative 197 (Equation 33) <1998JOC3599>. 

Because of their predictable behavior and reactivity, thioacyl isocyanates comprise the bulk of this work, and extensive studies of their [4 -I- 2] reactions with olefins, enamines, enol ethers, thioacyl isocyanates, imines, carbodiimides, isocyanates, azirines, /3-enaminoke-tones, dianils, azines, hydrazones, imidazoline-4,5-diones, aryl cyanates, disubstituted cyanamides, aldehydes, ketones, ketenes, alkyl or aryl iminodithiocarbonates, and the carbon-carbon double bond of ketenimines have been detailed. In an extensive comparative study of the [4 + 2] cycloaddition reactions of thioacyl isocyanates, the heterocu-mulenes bearing strong electron-withdrawing substituents were found to be more stable and less prone to participate in cycloaddition reactions. Representative examples are summarized in Scheme 9-IV. 

Far more interesting are the elimination sequences which lead to the generation of reactive heterocumulenes (ketenimines, carbodiimides, isocyanates, isothiocyanates) or 1,3-dipoles (nitrile oxides, nitrile imides, nitrile... 

Photoreactions have also been observed between 3-phenyl-2/f-azirines and ketenes, carbodiimides, isocyanates as well as isothiocyanates. The isocyanates and their thio analogs react with the C-O and C-S double bonds, respectively, to give 79, 80, and 81, and not with the C-N double bond. ... 

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