Asymmetric phenylation

The reaction of a halide with 2-butene-1,4-diol (104) affords the aldehyde 105, which is converted into the 4-substituted 2-hydroxytetrahydrofuran 106, and oxidized to the 3-aryl-7-butyrolactone 107[94], Asymmetric arylation of the cyclic acetal 108 with phenyl triflate[95] using Pd-BINAP afforded 109, which was converted into the 3-phenyllactone 110 in 72% ee[96]. Addition of a molecular sieve (MS3A) shows a favorable effect on this arylation. The reaction of the 3-siloxycyclopentene 111 with an alkenyl iodide affords the. silyl... 

The name found its origin in the fact that the first dyes known were all derived from quinoline as, for example, 2,2 -cyanine (Scheme 1). In the case of an asymmetrical or symmetrical dye involving one or two nuclei that are different from the quinoline ring, the name of the nucleus becomes the prefix in the name of the dye. So 3.3 -dimethyl-4-phenyl thiazolo cyanine is the dye of structure 1 and 3.1 -dimethyl 4-phenyl thiazolo 2 -cyanine is represented by the formula structure 2 (Scheme 2). 

Researchers at Du Pont used hydroquinone asymmetrically substituted with chloro, methyl, or phenyl substituents and swivel or nonlinear bent substituted phenyl molecules such as 3,4- or 4,4 -disubstituted diphenyl ether, sulfide, or ketone monomers. Eor example,... 

Direct Blue 218 had reported sales of 623 t valued at 4.4 million ia 1987. It is produced from Direct Blue 15 (76) by metallizing and elimination of methyl groups from the methoxide to form the copper complex. Direct Blue 15 (76) is prepared by coupling o-dianisidine [119-90-4] to two moles of H-acid (4-amiQO-5-hydroxy-2,7-naphthalenedisulfonic acid) under alkaline pH conditions. Other important direct blues iaclude Direct Blue 80 (74), (9-dianisidine coupled to two moles of R-acid (3-hydroxy-2,7-naphthalenedisulfonic acid [148-75-4]) followed by metallizing to form a bis copper complex, and Direct Blue 22 (77), an asymmetrical disazo dye, prepared by coupling o-dianisidine to Chicago acid [82-47-3] and 2-naphthol. Direct Blue 75 (78) is an example of a trisazo dye represented as metanilic acid — 1,6-Q.eve s acid — 1,6-Q.eve s acid — (alb) Ai-phenyl J-acid. 

The addition of methylmagnesium iodide to 2-phenylpropanal is stereoselective in producing twice as much syn-3-phenyl-2-butanol as the anti isomer (entry 5). The stereoselective formation of a particular configuration at a new stereogenic center in a reaction of a chiral reactant is called asymmetric induction. This particular case is one in which the stereochemistry can be predicted on the basis of an empirical correlation called Cram s rule. The structural and mechanistic basis of Cramls rule will be discussed in Chapter 3. 

The mechanism of the asymmetric alkylation of chiral oxazolines is believed to occur through initial metalation of the oxazoline to afford a rapidly interconverting mixture of 12 and 13 with the methoxy group forming a chelate with the lithium cation." Alkylation of the lithiooxazoline occurs on the less hindered face of the oxazoline 13 (opposite the bulky phenyl substituent) to provide 14 the alkylation may proceed via complexation of the halide to the lithium cation. The fact that decreased enantioselectivity is observed with chiral oxazoline derivatives bearing substituents smaller than the phenyl group of 3 is consistent with this hypothesis. Intermediate 13 is believed to react faster than 12 because the approach of the electrophile is impeded by the alkyl group in 12. 

The asymmetric synthesis of (4i ,9S, 9ai )-4-phenyl-l-trimethylsilyloxy-9-vinylperhydropyrido[2,l-c][l,4]oxazine by a high level of stereoselectivity in the cyclization of (3i ,5i )-5-phenyl-3-phenylsulfanyl-4-(6-trimethylsila-nylhex-4-enyl)-2-trimethylsilyloxymorpholine was rationalized via AMI calculations (98T10309). 

A similar but asymmetric variant of the reaction, involving the radical addition of alkyl iodides and trialkylboranes to chiral azirine esters derived from 8-phenyl-menthol and camphorsultam, in the presence of a Cu(i) catalyst, has subsequently been reported [64]. The diastereoselectivity of the addition is variable (0-92% de)... 

With the stcrically constrained /(-amino alcohols N-P asymmetric amplification phenomena were observed similar to the effects found with 3-e.Y0-(dimethylamino)isoborneol (vide supra). Thus, alkylation of benzaldehyde with diethylzinc, catalyzed by a partially resolved catalyst N-P, gives 1-phenyl-1-propanol with an enantiomeric excess, which impressively exceeds the optical purity of the catalyst employed12. 

Similarly, (A )-( )-3-(2-methoxymethyl-l-pyrrolidinyl)-l-phenylpropene118 121, after lithia-tion and addition of acetone, acidic hydrolysis and oxidation of the intermediate lactol, gives (5)-dihydro-5,5-dimethyl-4-phenyl-2(3/f)-furanone with 98% ee and 54% overall yield. Thus, these sequences constitute asymmetric homoaldol addition. 

Trimethyl(l-phenyl-2-propenyl)silane of high enantiomeric excess has also been prepared by asymmetric cross coupling, and reacts with aldehydes to give optically active products in the presence of titanium(IV) chloride. The stereoselectivity of these reactions is consistent with the antiperiplanar process previously outlined75. 

---