Isocyanates alkenyl

The 5-(2-alkenyloxy)thiatriazoles on thermal degradation gave alkenyl isocyanates by a presumed allylic rearrangement of the expected 2-alkenyl cyanates.54 Although the data do not exclude decomposition via intramolecular cyclic attack at the 4-position in the ring followed by very rapid decomposition of the 4-substituted thiatriazolines, these... 

Ketimines containing a hydrogen atom adjacent to the C=NH group form alkenyl isocyanates upon treatment with phosgene [1772] ... 

Another application of the [2+2+2] cycloaddition used alkenyl isocyanates 441 and terminal alkynes 390 for the formation of izidine alkaloid skeletons 442 and 443 with a lactam and a vinylogous amide moieties, respectively (Scheme 2-48). ... 

Scheme 2-48. [2+2+2] Cycloaddition of alkenyl isocyanates and terminal alkynes.

Figure 2-14. Proposed mechanism for the [2+2+2] cycloaddition of alkenyl isocyanates with...

Alkyl and Alkenyl Isocyanates Phosgene as carbonylation reagent... 

Another [2+2+2] cycloaddition reaction, using alkenyl isocyanates and alkynes, affords the vinyl amides 195 and 196 in good yields. The catalysts system used is [RhCl(C2H4)]2... 

Terminal alkynes react similarly with alkenyl isocyanates. In the presence of chiral phosphoramidites as ligands the corresponding cycloadducts are obtained. For example, from the alkenyl isocyanate 197 and the heterocyclic alkyne 198 the cycloadducts 199 and 200 are obtained in 85 % yield (91 % e,e) . 

Yu, R. T., Rovis, T. (2006). Enantioselective rhodium-catalyzed [2-I-2-I-2] cycloaddition of alkenyl isocyanates and terminal alkynes application to the total synthesis of (+)-lasubine II. Journal of the American Chemical Society, 128,12370-12371. 

Use of the phosphoramidite ligand (-)-199 proved to be crucial for the enantioselective rhodium-catalyzed crossed [2 + 2 + 2] cycloaddition of alkenyl isocyanate 197 with phenylacetylene 198, which provided the vinylogous amide 200 in 62% yield (98% ee). Thereafter, cycloaddition product 200 underwent a diastereoselective hydrogenation followed by a Mitsunobu reaction to complete the total synthesis of (+)-lasubine II (201). 

Here, the [2 + 2 + 2] cycloaddition of alkenyl isocyanate 202 and 1-octyne was promoted efficiently by the rhodium/(/ )-203 catalyst to give indolizinone 204 in 59% yield (91% ee). Thereafter, a highly diastereoselective hydrogenation followed by Barton-McCombie deoxygenation provided (—)-209D (205). Considering that... 

The formation of cyclic nitrones (150) from pericyclic mechanism. Kinetic and computational studies have provided evidence for the involvement of a novel pseudo-pericyclic electrocyclization in the conversion of o-vinylphenyl isocyanates into quinolin-2-ones. " Such reactions have also provided evidence of torquoselectivity in a 6jt system. Hash vacuum thermolysis of triazoles (151) has been found to afford dihydroquinolines (155), presumably by generation of a-oxoketenimines (152) which can undergo a [1,5]-hydrogen shift to the o-quinoid imines (153)7(154) and subsequent electrocyclization (see Scheme 57). 

The synthesis of the module is provided in Scheme 10.5 (Kushner et al. 2007). Double alkylation of ethyl acetoacetate followed by guanidine condensation afforded alkenyl-pyrimidone intermediate 24 (Kushner et al. 2007). Isocyanate 25 was coupled to pyrimidone 24 to yield 26. Upon dimerization in DCM, RCM effectively cyclized the two UPy units (Mohr et al. 1997 Week et al. 1999). A one-pot reduction and deprotection through hydrogenation using Pearlman s catalyst gave diol module 27. Finally, capping 27 with 2-isocyanatoethyl methacrylate at both ends provided the UPy sacrificial cross-linker 28, which was thoroughly characterized by H- and C-NMR, Fourier transform IR (FTIR), and mass spectrometry. 

Japanese workers prepared examples of 2-alkenyl-4,5-oxazolediones 40a and 40b, which are key intermediates in the synthesis of alkenoyl isocyanates 41a and 41b (Scheme 6.13). These reactive monomers are precursors to a variety of functionalized polymers including instantaneously curable compositions. Thus, reaction of oxalyl chloride with acrylamide 39a or methacrylamide 39b affords 40a and 40b isolated as hydrochloride salts in high yields. Subsequent decomposition of the 2-alkenyl-4,5-oxazolediones in the presence of a metal halide or synthetic zeolite affords 41a and 41b contaminated with varying amounts of 42a and 42b. The synthesis and reactions of other 2-substituted 4,5-oxazolediones have been described independently by Speziale and co-workers ° and Sasaki and co-workers. ... 

Full details42 have been published on the conversion of enynes into iminocyclopentenes using a titanium precatalyst in the presence of BuLi and TESCN (equation 9) the resulting iminocyclopentenes can be hydrolysed to cyclopentenones or reduced to allylic silyl-amines. In a related protocol43, the tandem insertion of TMSCN and alkenes, alkynes, ketones or isocyanates into zirconacyclo-pentanes or -pentenes leads to cyclopentylamines carrying an a-alkyl, -alkenyl, -1-hydroxyalkyl or -carboxamide substituent, respectively (equation 9). 

An alternative route to chiral p-lactams was provided by reactions of electron-deficient isocyanates with chiral nucleophilic alkenes such as vinyl ethers or vinyl acetates. Chlorosulfonyl isocyanate (CSI), a commonly used reactive isocyanate [34], undergoes stereospecific 5-yn-addition to alkenes. The chlorosulfonyl group can subsequently be reductively removed from the nitrogen atom. It has been shown that reactions between CSI and (Z)- and ( )-alkenyl ethers stereoselectively give cA-3,4-disubstituted azetidinones from (Z)-olefins and tmns-3,4-... 

The intra- and intermolecular carbon—heteroatom bond forming reactions using alkenyl epoxides and aziridines have been utilized for the synthesis of heterocyclic compounds.261 There are two major processes for the preparation of heterocycles using these substrates, as illustrated in Scheme 192 (a) intramolecular allylation of alkenyl epoxides and aziridines with Y—H and (b) intermolecular cycloaddition of vinyl epoxides and aziridines with the hetero-cumulenes 627, such as isocyanates, carbodiimides, and isothiocyanates.270... 

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