Unprotected compounds

Fluorination of adenine derivatives using elemental fluorine (1% F2 in Fie delivered at a rate of 5-10 j.mol F2 min ) gave the C-8 fluoro analogues in moderate yields <1996JA10408>. Although chloroform was the optimum solvent, this was not suitable for less-soluble, unprotected compounds and ethanol was substituted, although a reduction in yield was observed (Scheme 13). 

The y-amino-p-hydroxy acid derived oxazolidinones 55 are prepared from the corresponding N-unprotected y-amino-p-hydroxy ester derivatives by reaction with phosgene,1119,391 carbonyl diimidazole,[41] or benzyl chloroformate.[86] Alternatively, cyclization is obtained from the N-carbamate protected derivatives, i.e. from the TV-isopropenyloxycarbonyl derivatives under heating,[381 or from the TV-Boc or N-Z derivatives under basic conditions. [68 81 87] By analogy, the p,y-diamino acid analogue is converted into the imidazolidinone 57 by treatment of the unprotected compound with phosgene.[83 88]... 

Arylpiperazines can be prepared in a one-pot procedure by ipso SNAr of piperazine derivatives with //6-fluoroarene complexes la, 33a,b,d. Indeed, piperazine derivatives react with fluorobenzene derivatives in DMSO in the presence of K2CO3 at 80 °C to give, after 2.5 h, complexes 3m and 3k (Nu = piperazine) in good yields (Scheme 18) [34]. Piperazine itself may be used as a nucleophile and gives the monoarylpiperazine derivative uncontaminated by any symmetrical N,N -bis(aryl)piperazine, allowing the direct preparation of unprotected compounds. 

Cyclisation of (87) occurs on irradiation in the presence of triethylamine. The process involves SET, loss of iodide and attack by the resulting a-enone radical on the acetylenic bond. The unprotected compound (88) does not cyclise. Irradiation of N-(chloropyridyl)enaminones (89) and (90) in the presence of triethylamine yields the tetrahydrocarbazolones (91) and (92), with the regioselec-tivity being dependent on the solvent system used. Additionally the N-ethyl-enaminone (90) gives solvent incorporated products (93) or (94) in methanol or benzene respectively. ... 

The substrate-induced diastereoselectivity was investigated using an (R)- or (S)-1-phenylethyl group as a chiral auxiliary on the amide nitrogen. The reactions with the unprotected compounds went smoothly and diastereomeric mixtures were obtained in excellent yield and syn diastereoselectivity (> 99% syn) (entries 6-8). The results were better than those obtained with the butylamides. The facial selectivity was in the range of about 8 1. The protection of the hydroxyl group lowered both the facial selectivity and the yield (entry 8). 

The ability to protect an aldehyde in the presence of a ketone allows chemical reactions of the ketone group without competitive reactions that would occur in the original unprotected compound. For example, the Wolff-Kishner reduction converts the carbonyl group to a methylene group. 

The synthesis of block copolymers by macromonotner RAFT polymeriza tion has been discussed in Section 9.5.2 and examples are provide in Table 9.9. RAFT polymerization with thioearbonylthio compounds has been used to make a wide variety of block copolymers and examples arc provided below in Tabic 9.28. The process of block formation is shown in Scheme 9.59. Of considerable interest is the ability to make hydrophilic-hydrophobic block copolymers directly with monomers such as AA, DMA, NIPAM and DMAEMA. Doubly hydrophilic blocks have also been prepared.476 638 The big advantage of RAFT polymerization is its tolerance of unprotected functionality. 

The most specific biomarker of exposure to methyl parathion is the presence of the compound in serum or tissue. This is an especially good biomarker for detection shortly after acute exposure. For example, methyl parathion levels were detected in the sera of five men who were exposed for 5 hours in a cotton field 12 hours after it was sprayed with methyl parathion. The route of exposure was dermal, through unprotected hands. Serum levels averaged 156 ppb after 3 hours of the 5-hour exposure, and averaged 101.4 and 2.4 ppb at 7 and 24 hours postexposure, respectively (Ware et al. 1975). 

FIGURE 26.58 Abrasion of two natural rubber (NR) tread compounds, one unprotected, the other with two parts Nonox ZA on a knurled Aluminum and a knurled steel surface, respectively, in the presence of (a) magnesium oxide (MgO) powder and (b) a dust mix of Fuller s earth and alumina powder. (Deduced from Schallamach, A.,Appl. Pol. Sci., 12, 281, 1968.)... 

FIGURE 26.59 Time record of the abrasion loss on a standard Akron grinding wheel in nitrogen and air of a natural mbber (NR) tread compound (a) unprotected and (h) protected with an antioxidant. (From Schallamach, A., Appl. Pol. ScL, 12, 281, 1968.)... 

As for the synthesis of 5-e/j/-KDG, compound 6 seemed to be a suitable precursor of the methyl ester of 5-deoxy-KDG 20 since only the C-5 hydroxyl was unprotected. In this case the key step was not the epimerization but the removal of that hydroxyl. Our attempts of radicalar deoxygenation of 6 were unsuccessful because the intermediate radical was intramolecularly trappy by the C-2.C-3 double bound. Therefore we first reduced the double bond and then converted the resulting diastereoisomeric alcohols 14 into the corresponding triflates 15 which were submitted to the action of sodium iodide. Finally the iodides 16 Aus obtained were hydrogenolyzed in the presence of diisopropylethylamin to give 17. 

Grignard reagents are quite restricted in the types of functional groups that can be present in either the organometallic or the carbonyl compound. Alkene, ether, and acetal functionality usually causes no difficulty but unprotected OH, NH, SH, or carbonyl groups cannot be present and CN and NOz groups cause problems in many cases. 

Moreover, Kim and coworkers have shown that a-amino-butyrolactones can be synthesized by a related process employing the amino acid homoserine with an unprotected hydroxy functionality [31]. In a more recent publication by the same research group, morpholin-2-one derivatives of type 9-37 have been prepared (Scheme 9.6) [32]. Herein, glycolaldehyde dimer 9-32 acts as a bifunctional compound, which first reacts with the a-amino acids 9-33 to give the iminium ions 9-34,... 

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