2-phenyl substituted oxazolines

The structure of the phenyl-substituted oxazoline 143 a was verified by X-ray crystal structure analysis. In most cases the reaction gave better yields of 143 and 144 when performed in acetonitrile than in DMF [87]. 

In contrast to the above additions A-allyl- and substituted A-allyl-amides, -urethanes, -ureas and -thioureas undergo intramolecular cyclization only in 6(3-96% sulfuric acid to give the corresponding oxazolinium and thiazolinium salts. Treatment of these cations with base yields 2-oxazolines and 2-thiazolines in moderate to good yields. The reaction is illustrated by the conversion of A-2-phenylallylacetamide (342) into 2,5-dimethyl-5-phenyl-2-oxazoline (343) in 70% yield 70JOC3768) (see also Chapter 4.19). 

Aziridines 180 (Scheme 3.65) react with acetonitrile and BF3 Et20, a Lewis catalyst, to give imidazolines 181 in 65-95% yield [98], Under the same reaction conditions, however, the C-3 phenyl-substituted aziridine 182 (Scheme 3.66) afforded oxazoline 183 in 59% yield [97]. 

Optimal selectivities of cinnamate aziridines are provided by the phenyl-substituted bis(oxazoline) (55d). In contrast, /ra .v-p-mcthyl styrene proved to be most selective with ferf-butyl substituted 55c and acetonitrile as solvent, Eq. 56, conditions that afford the cinnamate ester-derived aziridine in only 19% ee. Styrene is a poor substrate for this catalyst and provides the opposite antipode as the major enantiomer from the same ligand, Eq. 57. 

Gu, R.-L., Lee, I.S. and Sih, C.J., Chemo-enzymatic asymmetric synthesis of amino acids. Enantioselective hydrolyses of 2-phenyl-oxazolin-5-ones. Tetrahedron Lett., 1992, 33, 1953-1956 Crich, J., Brieva, R., Marquart, P., Gu, R.-L., Flemming, S. and Sih, C.J., Enzymic asymmetric synthesis of a-amino acids. Enantioselective cleavage of 4-substituted oxazolin-5-ones and thiazolin-5-ones. J. Org. Chem., 1993, 58, 3252-3258. 

Epoxides also participate in the Ritter reaction with nitriles. An investigation of the ring opening of several alkyl-substituted glycidic esters and amides 181 showed that this transformation occurs with inversion and is completely regiospecific. ° Esters appeared to be somewhat more reactive than amides. However, phenyl-substituted glycidic esters and amides 184 are almost totally nonstereoselective. In addition, the oxazolines 186 are isolated in low yield due to the propensity of intermediate 185 to generate an aldehyde byproduct 187 (Scheme 8.53). 

Klumpp and co-workers have recently shown299 that 2-oxazolines, which are prone to ring opening, when bearing a phenyl substituent at C(5) are capable of alkylating weak nucleophiles under superacidic conditions to yield phenyl-substituted amides [Eq. (5.111)]. Benzene and even ortho-dichIorobenzene could be alkylated in excellent yield. The diprotonated ring-opened intermediate 75 has been invoked to interpret the reactions. 

Remko, M., Duijnen P.Th. van and Swart M., Theoretical study of molecular structure, tau-tomerism, and geometrical isomerism of N-methyl and N-phenyl substituted cyclic imidazolines, oxazolines and thiazolines. Struct.Chem. (2003) 14 271-278. 

Enantioselective Aziridination of Alkenes. Copper complexes with neutral methylenebis(oxazoline) ligands (1) and (2) have also been employed as enantioselective catalysts for the reaction of alkenes with (Al-tosylimino)phenyliodinane, leading to A-tosylaziridines. The best results have been reported for cinna-mate esters as substrates, using 5 mol % of catalyst prepared from CuOTf and the phenyl-substituted ligand (2) (eq 6). The highest enantiomeric excesses are obtained in benzene, whereas in more polar and Lewis basic solvents, such as acetonitrile, the selectiv-ities are markedly lower. The chemical yield can be substantially improved by addition of 4X molecular sieves. Both Cu - and Cu"-bisoxazoline complexes, prepared from Cu or Cu triflate, respectively, are active catalysts, giving similar results. In contrast to the Cu-catalyzed cyclopropanation reactions discussed above, in which only Cu complexes are catalytically active, here Cu complexes are postulated as the actual catalysts. ... 

Next, Evans et al. [15] reported that Cu-based catalysts were superior in the Diels-Alder reaction of the oxazolidinone 9 with cyclopentadiene 8. ITie (5,5)-bis(oxazo-line)-Cu(II) and -Zn(II) complexes were very effective catalysts of the reaction. The optimum tert-butyl ligand 13-Cu(II) complex afforded (2S)-endo-ll with > 98 % ee. In contrast, the optimum catalyst system for the phenyl-substituted ligand 12-Zn complex afforded the enantiomeric (R) product, (2R)-endo-ll, with 92 % ee. The different direction of asymmetric induction was explained in terms of the geometry of cata-lyst-dienophile complexes at the corresponding metal centers. The bis(oxazoline)-Zn(II) complex-catalyzed reaction proceeded via the tetrahedral chiral Zn-dienophile complex VIII, in a manner similar to the bis(oxazoline)-Mg catalyst reported by Corey [13], whereas the reaction catalyzed by the cationic bis(oxazoline)-Cu complex proceeded via the square-planar Cu(II)-dienophile intermediate VII, so the diene preferred to approach from the opposite si face of the bound dienophile with s-cis configuration, avoiding steric repulsion by one of the tert-butyl substituents on the oxazoline rings. 

Evans, D.A., Johnson. J.S.. Burgey. C.S., and Campos, K.R., Reversal in enantioselectivity of tert-butyl versus phenyl-substituted / z4 (oxazoline) copper(II) catalyzed hetero Diels-Alder and ene reactions. Crystallographic and mechanistic studies. Tetrahedron Lett., 40, 2879, 1999. 

Kagiya et al. determined the reactivity ratios of 2-phenyl-2-oxazoline (Mx) in copolymerization with other substituted oxazolines in N,N-dimethylacetamide at 135 °C19). The reported values of r2 and r2 are collected in Table 15.4 l/rt (= k12/kn) and... 

With dimethyl fumarate, methyl acrylate, and methyl methacrylate as dipolarophiles, substituted pyrrolines are obtained.52-54 In contrast, the reaction of 2-phenyl-2-oxazolin-5-onium perchlorate with benzyl-ideneaniline follows a different course to give the imidazolin-4-one (24).55... 

Phenyl-2-oxazolin-5-one undergoes ready 4,4-substitution with activated alkyl halides. " Oxidation of the a,a-dialkylated hippuric acids obtained from hydrolysis of the oxazolinones then yields symmetrical ketones (Scheme 17). 

Alkoxy-substituted benzoyl-PEIs having Cs-Cij alkyl groups formed self-assembly of hexagonal, columnar, 2D phase.Molecular stmctures of self-assembling from poly (2-(3,4-bis(n-alkoxy)phenyl)-2-oxazoline)s were systematically investigated with regard to the DP and alkoxy chain... 

N-phenylmaleimide. The formation of 2-phenacylidene-3-methyl-5-phenyl-l,3-oxazoline by the treatment of the salt (158) with sodium hydride in DMSO was considered to proceed through the thiocarbonyl ylide (159). However, the thiocarbonyl ylide (160), which in a similar manner to that mentioned above was generated from its corresponding dithiolanium salt, instead underwent a spontaneous ring-closure, yielding the spiro-compound (161). The thiocarbonyl ylide dipolar characteristics of phenyl-substituted thieno[3,4-c]pyrroles, phenyl-substituted thieno[3,4-c]thiophens, and the thieno[3,4-/)benzo[c]thiophen (162) have been substantiated by their reactions with dipolarophiles. The first representative (164) of the hitherto... 

A more expected difference between platinum oxide and palladium-on-carbon was found in the hydrogenolysis of 5-phenyI-2-(3,4-dimethoxybenzyI)-2-oxazoline. Cleavage occurred at the benzyl-oxygen bond over both catalysts, but over platinum, the less substituted phenyl group was saturated as well (78). 

When trimethylaluminum reacted with 3-methyl-cyclohexa-2,5-dienone in the presence of chiral oxazoline ligands 86, the conjugate addition proceeded efficiently at the less-substituted double bond with up to 68% ee (Scheme 43).129,129a tw0 0 0-substituents on the phenyl ring of ligands 86 were considered to be important for selectivity. 

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