Isocyanates condensation with

Surprisingly, however, monoalkylaminium cation radicals 104 have not been studied well. Newcomb found that they could not be prepared from respective PTOC carbamates due to instability of the precursors, nevertheless, the problem was solved via the isocyanate condensation with a different thio-hydroxamic acid 105a, as shown in Scheme 44. These deriva-... 

Alkyl uracyls have been known for some time to act as diuretic agents in experimental animals. The toxicity of these agents precluded their use in the clinic. Appropriate modification of the molecule did, however, yield diuretic agents with application in man. Reaction of allylamine with ethyl isocyanate affords the urea, 89 (the same product can of course be obtained from the same reagents with reversed functionality). Condensation with ethyl cyanoacetate affords aminotetradine (90). In... 

Ethyl formate, condensation with 2-methylcydohexanone, 48, 41 purification of, 48, 42 Ethyl isocyanate, reaction with N,N-dimethy 1-1,3-propanediamine,... 

Formate esters behave as typical carbonyl compounds in reactions with a number of ylides, eliminating phosphine oxide and forming vinyl ethers, e.g. (33).35 Stabilized phosphoranes are able to condense with the carbonyl group of cyclic thioanhydrides (34).38 Quinoline derivatives, e.g. (35), are obtained from the condensation of dicar-boalkoxy-ylides with isocyanates.37 Benzoyl isothiocyanates and keto-phosphoranes give quantitative yields of (36), which are unreactive in Wittig reactions but can be readily oxidized by selenous acid.38 The products obtained from reactions (Scheme 9) with the triazolinedione (37) depend upon the stability of the ylide used.39... 

The condensation of isocyanate esters with diguanides proceeds in an entirely comparable manner, providing a corresponding series of s-triazin-2-ones (i.e. substituted ammelines) 378). However, since loss of water from carbamoyl-intermediates [e.g. RNHCONH C( NH)NH C( NH) -NH2] occurs much less readily than loss of hydrogen sulphide from their thiocarbamoyl-analogues, melamines are not formed in this reaction 378). The production of adducts from phenyl isocyanate and tetra-. 

The two key isocyanates that are used in the greatest volumes for polyurethane polymers are toluene diisocyanate (TDl) and methylene diphenyl diisocyanate (MDl). Both isocyanates are produced first by nitration of aromatics (toluene and benzene, respectively), followed by hydrogenation of the nitro aromatics to provide aromatic amines. In the case of MDl, the aniline intermediate is then condensed with formaldehyde to produce methylene dianiline (MDA), which is a mixture of monomeric MDA and an oligomeric form that is typical of aniline/formaldehyde condensation products [2]. The subsequent reaction of phosgene with the aromatic amines provides the isocyanate products. Isocyanates can also be prepared by the reaction of aromatic amines with dimethylcarbonate [3, 4]. This technology has been tested at the industrial pilot scale, but is not believed to be practiced commercially at this time. 

Diamines condense with alkoxycarbonyl isocyanates (R02C—N=C=0), dialkyl iminodicarboxylates [HN(C02Me)2] or urea to give triazepinediones (495). 

Polyhydroxylated piperidines such as are of interest as glucosidase inhibitors. Antoni Riera, also of the University of Barcelona, has developed (J. Org. Chem. 2005, 70,2325) a route to 16 from the readily-available enantiomerically-pure epoxide 11. Condensation with ally isocyanate 12 followed by cyclization gave 13, which was further cyclized by a Grubb s catalyst (unspecified) to 14. Protection set the stage for face-selective dihydroxylation, to give 15. Several other piperidines having other polyhydroxylation patterns were also prepared from 14. 

Isocyanates. It has been reported recently from three laboratories 7 . that ethylene oxide and styrene oxide condense with certain organic isocyanates, among them cyclohexyl. 

The first step in the overall synthetic scheme (Scheme 6) is the condensation of an appropriate carboxylic acid with trifluoroacetaldehyde. The carboxylic acid is chosen to impart specificity for the target enzyme. In one example,[28 the dianion of cyclohexanepropanoic acid (29) was formed by the addition of LDA and then quickly condensed with trifluoroacetaldehyde to form the p-hydroxy acid 30 as a racemic mixture of erythro- and threo-isomers. The p-hydroxy acid 30 is then protected with TBDMSOTf forming 31. Diphenyl phosphorazidate, TEA, and benzyl alcohol were then utilized in a Curtius rearrangement of the protected alcohol 31, which proceeds through an isocyanate intermediate that yields the protected amino alcohol 32 upon reaction with benzyl alcohol. In order for this step to occur at an appreciable rate, a second equivalent of triethylamine had to be added. The amino alcohol 32 was then deprotected and coupled with Boc-Phe-Leu-OH to give the trifluoromethyl alcohol 33, which was oxidized to the corresponding trifluoromethyl ketone 34 as a 1 1.2 mixture of diastereomers using the Dess-Martin periodinane procedure. Thus far, the compound shown in Scheme 6 is the only compound that has been synthesized by this method, but it is reasonable to assume that many other similar fluoro ketones can be produced by this scheme. 

Cyclization of side chain nitriles has found extensive use in the synthesis of benzocyclobutenes (70 n = 2),104 the versatile synthons which open on mild thermolysis to give o-quinodimethanes for inter- and intra-molecular [4 + 2] trapping.108 The nitrile group in (70) can be manipulated into a variety of functionalities for appending the dienophile portion. For example, in the synthesis of chelidonine, the nitrile (71) was converted, by hydrolysis followed by Curtius degradation and reaction of the formed isocyanate with benzyl alcohol, to a urethane (72). The latter was then condensed with a benzyl bromide to get the compound (73), which was elaborated further as shown in Scheme 14.109... 

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