Asymmetric 1-phenyl-1,3 butadiene

Formation of 16, 14.6.1.2 CgH5CH=CHCH=CH2 (I -phenyl-butadiene) Asymmetric hydrosilylation of 16,... 

Starting from these substituted dienes, asymmetric syntheses of optically active polymers are possible, since the chirality of the asymmetric carbon atoms of the main chain is determined by the local environment. Indeed these syntheses have been successfully carried out with many of them. The synthesis of optically active polysorbates by Natta et al. dates back to 1960 (228), and is the first example of an asymmetric synthesis of homopolymers. A conclusive proof of the asymmetric induction was obtained by oxidative degradation of the polymers to succinic acid derivatives (229). This synthesis, as well as those performed with trans 1,3-pentadiene (230), 1-phenyl-butadiene (231), and l-phenyl-4-methy1-butadiene (146) have been carried out using optically active initiators. A new kind of asymmetric polymerization was obtained by Farina et al (232) by y-irradiation of trans-1,3-pentadiene included in (-)perhydrotriphenylene (XIX). 

Linear 1,3-dienes have also been subjected to the palladium-catalyzed asymmetric hydrosilylation (Scheme 12, Table 5). Reaction of 1-phenyl-l,3-butadiene 46a with HSiClj catalyzed by palladium-(/ )-(A)-PPFA 5a gave a mixture of regioisomeric allysilanes 47, and 48 and 49, in a ratio of 94 to 6, the major isomer 47 and the minor isomer 48 being 64% ee (S) and 30% ee (R), respectively (entry l).60 7r-Allylpalladium intermediate 50 was proposed for this hydrosilylation. Use of phenyldifluorosilane in place of trichlorosilane slightly improved the enantioselectivity (entry 8).58,61 Similar level of enantioselectivity (71-72% ee) was reported for the reaction using Ar-MOP ligand 37f (entry 11) and its dioctylated derivative 37g (entry 12).57a... 

This asymmetric end has the alkoxy group of alkyl vinylethers by cationic polymerization, phenyl group of styrene when either anionically or cationicaiiy polymerized, the vinyl group of butadiene under anionic catalysts to poly-1,2-butadiene, the ester and methyl of methylmethacrylate under anionic catalysis and the methyl of propylene by cationic catalysis. 

Section II, 1. Theoretical aspects of asymmetric polymerization have been discussed by Fueno and Furdkawa [T. Fueno, J. Furukawa J. Polymer Sci., Part A, 2, 3681 (1964)]. 1-phenyl-l,3-butadiene has been polymerized using (R)-2-methyl-butyl-lithium or butyl-lithium complexed with menthyl-ethyl-ether, yielding optically active polymers with [a] f, referred to one monomeric unit, between +0.71 and —1.79. Optical rotation dispersion between 589 m u and 365 mft is normal and the Drude equation constant is comprised between 255 raft and 280 raft [A. D. Aliev, B. A. Krenisel, T. N. Fedoiova Vysokomol. Soed. 7, 1442 (1965)]. 

Asymmetric hydroboration of 1-phenyl-1,3-butadiene (95) catalyzed by Rh-BINAP gave the corresponding optically active 1,3-diol 155 with 72% ee [89,90] (Scheme 2.15). Palladium-MOP complex also exhibited catalytic activity for the asymmetric hydroboration of but-l-en-3-yne (156), giving an optically active allenyl borane 157 [91]. 

Asymmetric Hydrosilylation of Alkenes. The palladium complex PdCl2[(/ )-(5)-PPFA] catalyzes the asymmetric hydrosilylation of norbornene, styrene, and 1,3-dienes (eq 3). The hydrosilylation of 1-phenyl-1,3-butadiene with Trichlorosilane proceeds regioselectively in a 1,4-fashion to give (Z)-1-phenyl-1-silyl-2-butene of 64% ee. 

A similar example is seen in the [Pd2(dba)3]-catalyzed hydroboration of 2-methyl-l-buten-3-ynes [274]. While PPhj and PPh2(CgF5) favor the 1,4-addition product allenylborane 100 all diphosphines yield the 1,2-addition product ( )-dienylborane 102 exclusively (Table 1-13). This remarkable difference in selectivity is explained based on an 1,3-enyne monophosphine complex 103 and an alkynyl diphosphine complex 104 as intermediates. Dppf exhibits the best product yield among the phosphines tested. Similar observation was noted in the asymmetric hydroboration (Scheme 1-44) [275]. The action of catecholborane on 1-phenyl-1,3-butadiene also proceeds regioselectively to give, after oxidation, anti-l-phenyl-l,3-butanediol... 

Stereoselective oxycarborative addition is also achieved in cycloaddition and cyclooligomeriza-tion reactions. Thus, hetero-Diels-Alder reactions of dienes and aldehydes are not only catalyzed by main group Lewis acids, but also by transition metal complexes 10°. Tris[3-(heptafluoropropyl-hydroxymethylene)-( + )-camphorato]europium [( + )-Eu(hfc)3] and similar vanadium complexes have been used as the chiral catalyst in [4 + 2] cycloadditions of various achiral and chiral dienes to aldehydes63 67-101. With achiral silyloxydienes only moderate asymmetric inductions are observed, however, with chirally modified dienes, high double diastereoselectivities are achieved. Thus, the reaction of benzaldehyde with 3-terf-butyldimethylsilyloxy-l-(/-8-phenvl-menthoxy)-l.3-butadiene (1) gives (2/ .6/ )-4-wf-bntyldimethylsilyloxy-5,6-dihydro-6-phenyl-2-[(17 ,3/ ,45 )-8-phenylmenthoxy]-2f/-pyran (2) in 95% yield with a diasteieoselectivity of 25 1 ss. After crystallization and hydrolysis with trifluoroacetic acid, optically pure (2/ )-2,3-di-hydro-2-phenyl-4-(4//)-pyranone (3) is obtained in 87% yield. 

The hydrocyanation of vinylarenes ° has been studied by a DuPont team using nickel catalysis. The hydrocyanation of 6-methoxy-2-vinylnaphthalene (2.219) affords the product (2.220), where the enantiomeric excess is strongly dependent upon the electronic nature of the bisphosphinite ligand (2.12). Hydrolysis of the nitrile (2.220) affords the nonsteroidal anti-inflammatory drug Naproxen. This nickel-catalysed procedure has also been applied with some success to the regiose-lective, asymmetric hydrocyanation of 1,3-dienes such as 1-phenyl-1,3-butadiene (2.221) to give the 1,2-adduct (2.222) with ees between 50 and 83%. ... 

The asymmetric hydrocyanation of dienes with substantial enantioselectivities has also been reported (Equation 16.10). Like the reactions of vinylarenes, these reactions have been reported with catalysts containing carbohydrate-derived phosphinites. Reactions of aryl-substituted dienes occur to form the products from 1,2-hydrocyanation. In addition to the reactions of purely acyclic dienes, such as 1-phenyl-l,3-butadiene, dienes containing an exocyclic vinyl group have been studied. These are substrates for products possessing... 

The trienamine-catalysed asymmetric Diels-Alder cycloaddition reaction of 2,4-dienals (77) with chiral phosphorous dienophiles (78) produced densely functionalized phosphonocyclohexene adducts (79) with excellent enantioselectivity (up to 99% ee) and good to high diastereoselectivity (up to >99 1) (Scheme 22). The thermal Diels-Alder reaction of l-phosphono-(3,4)-disubstituted-1,3-butadienes with maleimides and 4-phenyl-l,2,4-triazoline-3,5-dione produced polycyclic phosphonic acid derivatives. ... 

From the sign of rotation of the obtained acids, it is possible to determine the absolute configuration of the polymer. The occurrence of asymmetric induction in the polymerization of 1-phenyl-1,3-butadiene (LXXVII) in the presence of (/ )-2-methylbutyllithium or butyllithium (-)-menthylethylether complexe [206] was proved by ORD curves of these polymers but was not correlated with polymer conformation. 

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