Oxazolines, 2-aryl

Tomalia DA, Sheetz DP (1966) Homopolymerization of 2-alkyl and 2-aryl-2-oxazolines. J Polym Sci Part A Polym Chem 4 2253-2265... 

The requisite 2-aryl-2-oxazolin-4-ones can be synthesized using the procedure briefly described by Gordon for the preparation of 2-phenyl-2-oxazolin-4-one (65a)53K The method utilizes an intramolecular O-alkylation of an imide ambident anion. 

Ethoxyisoindolenone (50) and the 2-aryl-2-oxazolin-4-ones 65a, 65b, 65c, and 65d have UV absorption maxima which are contrasted with the UV absorption maximum of 2-ethoxypyrrolin-5-one (12) in Table 4s2. The UV absorption spectra of50, 65a, 65b, 65c, and 65d in general show intense 7r-7t bands. Only m-trifluoro-methylphenyloxazolinone 65d has what appears to be a slightly resolved n- r band as a shoulder on the n-n transition. 

Oxazolines 168 and bisoxazolines can be synthesised starting from a prop-2-ynylamide in a reaction catalysed by Pd/C or Pdh in the presence of O2 and CO <02JOC4450>. 4-Amino-2-aryl-2-oxazolines 170 can be synthesised electrochemically starting from jV-(l-amino-2,2-... 

Finally, ring-expanding carbonylation reactions using cobalt have been reported by various groups. In the first of these, the synthesis of 4,5-dihydro-l,3-oxazin-6-ones by a ring-expanding carbonylation reaction of 2-aryl-2-oxazolines with a cobalt catalyst has been reported by Xu and Jia. " This is the first example of the application of catalytic carbonylation to 2-oxazolines leading to the synthesis of an important intermediate in peptide synthesis (equation 32). On... 

Aryl oxazolines exhibit resistance to nucleophilic attack and can be lithiated with rc-BuLi. A range of methods are available for activation of the oxazoline group of the products to allow constructive conversion to other functional groups.142 104 A sequence of simple lithiations of 203 illustrate the potential of this method at the start of this synthesis of a precursor to a steroid.189... 

Degnan, A. P., Meyers, A. I. Total Syntheses of (-)-Herbertenediol, (-)-Mastigophorene A, and (+)-Mastigophorene B. Combined Utility of Chiral Bicyclic Lactams and Chiral Aryl Oxazolines. J. Am. Chem. Soc. 1999,121,2762-2769. 

Pd(OAc)2/2-ARYL OXAZOLINE CATALYSED SUZUKI COUPLING REACTONS OF ARYL BROMIDES AND BORONIC ACIDS... 

The palladium-catalysed Suzuki coupling reaction of aryl halides with arylboronic acids has proved to be a general and convenient synthetic tool employed in organic chemistry to prepare biaryl compounds.[1] The discovery and development of active and efficient palladium-catalyst systems have been the focus of great interest recently. New catalytic systems based on paUadium-oxazolines, such as 2-aryl oxazolines and 2,2 -(l,3-phenylene)bisoxazoline (Figure 4.1) have been developed for the coupling reaction. These catalytic systems have the potential to overcome... 

Alkoxyanthranilic acids have been prepared by regioselective amination of aryl oxazolines using diphenyl phosphorazidate (Scheme... 

Finally, Meyers et al. have carried out an asymmetric synthesis of (-)-podophyllotoxin involving conjugate addition to an aryl oxazoline (scheme 59) [129]. The penultimate step involves C-2 epimerisation favouring the cw-1,2-geometry. 

The barriers to rotation in N-aryl-oxazoline-2-thione 53 and N-aryl-imidazoline-2-thione 54 were evaluated by DNMR. The barrier was strongly dependent on the intracyclic heteroatom (85JCS(P2)273). Despite the relatively low barrier one should expected in N-aryl-oxazo-line-2-ones and N-aryl-oxazoline-2-thiones, several examples of atropi-somer separation were reported on the Whelk 01 column (96JC(A726) 91,96JC(A753)109)... 

XXXXII. The latter is cyclized to oxazoline XXXXIII by treatment with thionyl chloride. Oxazoline XXXXIII reacts with aryllithium or aryl Grignard reagent to produce the ort/zo-arylated oxazoline XXXXIV. This is further hydrolyzed with acid to the respective biphenic acid XXXXV [39,40], Scheme 18. 

Interestingly, the chemoselectivity of this catalytic system changed dramatically when using aryl oxazolines along with substituted allyl acetate 104. Thus, oxidative homocoupling reactions occurred under these reaction conditions (Scheme 9.37) [50]. Imidazole, pyrazole or thiazole derivatives could also be efEciently homocoupled. 

Meyers and colleagues described the palladium-catalyzed carbonylative synthesis of oxazolines as early as 1992 [268]. Aryl or enol triflates made from the corresponding ketones and phenols, and also aryl halides, were used as starting materials and coupled with amino alcohols to give chiral a,)S-unsaturated or aryl oxazolines in good yields. Later on, Perry s group performed systematic studies on this one-pot, two-step process for the preparation of oxazolines (Scheme 2.37) [269, 270]. 

For a review aryl oxazoline chemistry, see M.Reuman and A.I.Meyers, Tetrahedron, 1985, 837. 

Yang, D., Yip, Y.C., Wang, X.C. 1997. Oxidative cleavage of aryl oxazolines using methyl(trifluoromethyl)dioxirane generated in situ. Tetrahedron Letters 38(40) 7083-7086. 

Scheme 5.37 Ullmann coupling of L-alaninol-derived aryl oxazoline.

Linear polyethylenimine (LPEI), which contains only secondary amino functions, has been prepared in different ways. The one most used is the hydrolysis of poly(N-acyl ethyienimine), which is obtained by cationic polymerization of the corresponding N-alkyl or aryl oxazoline (see Chapter 4.24), (Scheme 5). This type of polymerization exhibits living characteristics so that polymers with controlled molecular weight and narrow distribution can be obtained. Consequently, the LPEI obtained from such a polymer will also have a... 

Meyers, A.I., Robichaud, A.], and McKermon, M.J. (1992) The synthesis of chiral a,P-unsaturated and aryl oxazolines from ketones and arols via their triflates and Pd-catalyzed CO and amino alcohol coupling. Tetrahedron Letters, 33, 1181—... 

Human rhinovirus inhibition Substituted aryl-oxazolines 326/1993... 

These reactions complement recently developed palladium(0)amination reactions [146,147,148] and related procedures using a copper(I) [149] - or ni-ckel(O) [151] - catalysis. As indicated above, the mild reaction conditions are compatible with a range of functional groups. Functionalized arylmagnesium chlorides such as 309 prepared by an I/Mg-exchange readily undergo addition reactions to aryl oxazolines. The addition-elimination of 309 to the -methoxy aryloxa-zoline followed by an ortHo-lithiation and substitution with ethylene oxide leads to a polyfunctionalized aromatic intermediate 310 for alkaloid synthesis (Scheme 4.68) [165]. 

Asymmetric versions of the cyclopropanation reaction of electron-deficient olefins using chirally modified Fischer carbene complexes, prepared by exchange of CO ligands with chiral bisphosphites [21a] or phosphines [21b], have been tested. However, the asymmetric inductions are rather modest [21a] or not quantified (only the observation that the cyclopropane is optically active is reported) [21b]. Much better facial selectivities are reached in the cyclopropanation of enantiopure alkenyl oxazolines with aryl- or alkyl-substituted alkoxy-carbene complexes of chromium [22] (Scheme 5). 

Prasad RS, Anderson CE, Richards CJ, Overman LE (2005) Synthesis of tert-leucine-derived cobalt oxazoline palladacycles. Reversal of palladation diastereoselectivlty and application to the asymmetric rearrangement of N-aryl trifluoroacetimidates. Organometallics 24 77-81... 

Scheme 1.24 Test reaction with sulfanylmethyl-, aryl-, and thiophene-oxazoline ligands.

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