Urethans carbonylation

Derivatization of cyclic urethanes with (B0C)20 makes the urethane carbonyl susceptible to hydrolysis under mild conditions and leaves the amine protected as a BOC derivative."... 

Figure 2. XPS C Is spectra for oligourethane based coatings (a) untested oligomer coating surface (b) interfacial coating surface after mechanically induced adhesion loss (c) interfacial coating surface after humidity induced adhesion loss. Spectral components A, B, C, and D attributed to methyl/methylene, ether, melamine, and urethane carbonyl carbons, respectively. Reproduced from Ref. 19, copyright 1984, American Chemical Society.

The negative VCD observed in dilute solution at the urethane C==0 stretching frequency, and the negative bias observed at higher concentrations is due to an intrinsic contribution from the urethane carbonyl stretch. In either the cis or trans conformation, the urethane C=0 stretch can generate current around an... 

Replacement of the urethane carbonyl function by an aromatic ring leads to a benzo-thiazole that is described as an immune function modulator. In an analogous approach to that used above, anilinothiol (63-1) is condensed with the thiocarbamoyl chloride (63-2) again in the presence of a base. This leads directly to frentizole (63-3) [66]. 

Isatin j8-thiosemicarbazones (97) readily give triazinoindoles (98) (72JMC277). Deprotonation of the amide (99) leads to ring closure on to the urethane carbonyl group to give (100). In a similar reaction (101 to 102) the lower reactivity of the t-butyl ester induces ring closure in the required direction (78CPB3080). 

When more than one amide is present, such as in the tripeptide Boc-Gly-Phe-Leu-OEt, a mild reagent will convert the less-hindered Gly-Phe bond into the thioamide while leaving the Phe-Leu bond, as well as the ester and urethane carbonyls, intact at room temperature to furnish Boc-Glyr )[C(=S)-NH]Phe-Leu-OEt. However, the attempted conversion of c-[-d-Lys-Gly-Phe-Leu-] into thioamide product failed using l. 9 Only with P2S5 did thioamide conversion take place, and multiple thionylation products were the result. 

On the other hand, the group of No wick [29] developed polyurea templates with the general structure 35 in order to nucleate parallel /1-sheet structures. They reported that in a model compound (36) the urethane carbonyls are hydrogen bonding to the adjacent NH and that the orientation of the bonding interactions is controlled by the size of the end substituent, in this case a phenyl group. They also recently prepared 37 and showed by NMR that it adopts mostly the proposed parallel /1-sheet conformation in chloroform [30]. 

Recently it has become clear that organozinc halides can also be formed in more polar solvents than tetahydrofuran, for example in dimethylformamide.19 Organozinc halides with a urethane protected (3-amino group appear to be much more stable in polar solvents. This increased stability is due to the inhibition of intramolecular coordination by the urethane carbonyl to the zinc atom, which in turn can lead to facile fl-elimination.20... 

To overcome the drawbacks associated with the application of non-urethane N-terminal blocking groups, a new strategy had to be developed which enables a biocatalyst to cleave a urethane structure without the need for a direct attack on the urethane carbonyl group. The principle was successfully realized by the introduction of the p-acetoxybenzyloxycarbonyl (AcOZ) [30] and thep-phenyl-acetoxybenzyloxycarbonyl (PhAcOZ) [31] groups (Fig. 9). 

Lithiation of both A/-phenyl- and 0-phenyl-urethanes has been reported. The ortho lithiadon of /V-r-bu-toxycaibonylaniline and subsequent addition to carbonyls, nitriles and several other electrophiles was first reported by Muchowski in 1980. In some cases the adduct cyclized by attacking the urethane carbonyl. Typical examples are shown in Scheme 17. Lithiation of an /V-r-butoxycarbonylaniline derivative served as one of two directed lithiation steps in Snieckus synthesis of anthramycin (17 Scheme 18). Treatment of phenothiazines with 2 equiv. of butyllithium affords an A(,o-dilithium species, but reaction with electrophiles occurs at both sites. Katritzky has shown that the sequence of N-lithiadon, car-bonation and o-lithiation protects the nitrogen from alkylation (Scheme 19). ... 

The hydrogen-bonded complexes of phenols with the model dipeptide 74 have been investigated . Complexation occurs at both the amide and urethane carbonyl groups. About 45% of the complexes are formed on the urethane functions, almost independent of the Brpnsted acidity of the phenols. When phenols are attached to the amide group, the intramolecular hydrogen bond seems to be broken. 

Major results. Figure 14.30 shows the relationship between relaxation time, T2, and amount of filler in solid racket propellant. Relaxation time decreases with filler load because the material becomes more rigid with increasing filler loading. Urethane carbonyl, and aromatic carbons were found among others in kaolin modified by urethane. Conformational changes in PMMA were found in a strongly inter-... 

Urethane and urea Amide bands coupled with the N-H stretching bands have been studied by many investigators to explore the relationship between intermolecular and intramolecular interactions and morphologies of polyether-urethanes (16, 18-20, 23-32) and polyether-urethane-ureas (15,17,21,22,33-37). The N-H groups serve as proton donors in the interactions. The possible proton acceptors in polyether-urethanes initially were assumed to be only the urethane carbonyls or polyether oxygens (16, 19, 23-27). Under these assumptions, complete phase separation characterized... 

The 1800-1500 cm-1 regions of the infrared spectra of PEUU 700 with 5, 25, and 50 wt % LiBr are shown in Figure 5. While the N-H stretching vibrational modes of the urethane and urea groups in PEUU 700 overlap, the carbonyl stretching Amide I vibrational modes are well separated. Previous studies (8,9) assigned the urethane carbonyl stretching vibrational modes in... 

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