Isocyanates, addition

Iodine azide, on the other hand, forms pure adducts with A -, A - and A -steroids by a mechanism analogous to that proposed for iodine isocyanate additions. Reduction of such adducts can lead to aziridines. However, most reducing agents effect elimination of the elements of iodine azide from the /mwj -diaxial adducts of the A - and A -olefins rather than reduction of the azide function to the iodo amine. Thus, this sequence appears to be of little value for the synthesis of A-, B- or C-ring aziridines. It is worthy to note that based on experience with nonsteroidal systems the application of electrophilic reducing agents such as diborane or lithium aluminum hydride-aluminum chloride may yet prove effective for the desired reduction. Lithium aluminum hydride accomplishes aziridine formation from the A -adducts, Le., 16 -azido-17a-iodoandrostanes (97) in a one-step reaction. The scope of this addition has been considerably enhanced by the recent... 

Iodine isocyanate addition to olefins / 22 Halogen azide addition to olefins / 24 Via epoxides and / -mesyloxy azides / 27 By addition of alkoxyamines / 29... 

On prolonged reaction with aryl isocyanates, the pyrido [ 1,2-a]pyrimidines (262) give pyrido[l,2-a]-s-triazines (266) in poor yield.328 The suggested pathway is the addition of the aryl isocyanate to form the 3,3-disubstituted product (263), which eliminates the ketene (265) the residual part of the molecule (264) reacts with an additional mol of aryl isocyanate to give 266. The ketene (265) forms the quinoline (267), by ring closure, which gives 268 by aryl isocyanate addition. The quinoline (267 R = CH2Ph, X = H) could be isolated. 

An interesting application of the isocyanate addition is a reaction which initially yielded carbodiimide that reacted with a simple enamine to give an intermediate leading in a hetero-Diels-Alder reaction to a phenanthridine derivative13 (equation 9). 

A more detailed quantitative study of the water-o-tolyl isocyanate reaction by Shkapenko et al. 51) showed that at 80° in dioxane solution and in the presence of triethylamine or other catalysts the consumption of the isocyanate was complete within a short period when only approximately half of the theoretical amount of carbon dioxide was released. The evolution of carbon dioxide proceeded from this point on at a slow rate. It was also demonstrated that by heating the reaction mixture to 100°, 30-35% of theoretical CO2 was released, and that this portion of the CO2 was given off by the decomposition of the carbamic acid anhydride formed from the acid and a second molecule of isocyanate. Additional tests showed that 4-5% of the isocyanate formed o-tolyl ammonium-W-o-tolyl carbamate, 18.7% of the water added remained unreacted, and that a trace of the free o-tolyl amine was also present. In addition, the presence of di-o-tolyl urea was proven. 

Table 1. Products of the isocyanate addition to triamino triazine.

There are a number of syntheses leading to the formation of urethane polymers. However, the most important commercial route is the isocyanate addition polymerization, the reaction between di- and polyfunctional hydroxyl compounds such as hydroxy-terminated polyethers or polyesters and di- or polyisocyanates. When difunctional reactants are being used, linear polyurethanes are produced and the reaction can be schematically represented as follows ... 

Another method for synthesis of useful derivatives of L-acosamine and L-daunosamine from rhamnal 23 was based on addition of chlorosulfonyl isocyanate to 2,3-unsaturated pyranosides 73 [66,67]. Since the anomeric alkyl substituent in this reaction ends up as the carbamate ester, aUyl glycoside securing easy deprotection was chosen for elaborating this reaction into large laboratory scale technical process. Method development for acosam-inal derivative 74 involved multiparameter optimization of the isocyanate addition step by exploration of the reaction response surface. The final daunosaminyl glycosylation synthon 76 was obtained in overall 35% yield (Scheme 12) [68]. 

Flucarbazone and propoxycarbazone can be prepared by various methods (a) Sulfonyl isocyanate addition (Scheme 2.6.2) [1, 17]. 

Brady et al. have reported an efficient method for catalytic phosphityla-tion of alcohols (14) with phosphoramidites (15) and isocyanate additives (Scheme 6). ... 

Investigations of isocyanate interacdiion with aqueous NaOH solutions [178] conducted by us estabhshed that triiscKyamu ates are formed with increase of scxlium hydroxide concentration above 20% and the output of isocyanate cychc trimer grows monotonically with the increase of sodium hydroxide concentration above 20%. There are three ion types in the aqueous alkah solutions, namely, Na, H3O, and OH, but it is reasonable to regard hydroxyl ion as the initiating species in isocyanate polsmierization. Hydroxyl ion in the acjueous alkali solutions is enclosed in a hydration sphere, but despite this it displays the initiating action in isocyanate addition polymerization reactions. 

Iodine isocyanate additions result in approximately 40% yields. The products can undergo typical reactions of the isocyanate group/ as above, and also ... 

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