Butadienes phenyl

The following observations have been made concerning the reaction of Z-1-phenyl-1,3-butadiene (A) and Z-4-phenyl-3-buten-l-ol (B) in 3-7 M H2SO4 and 0.5-3 M HCIO4 ... 

With 1-phenyl-1,3-butadiene, the addition is exclusively at the 3,4-double bond. This reflects the greater stability of this product, which retains styrene-type conjugation. Initial protonation at C-4 is favored by the feet that the resulting carbocation benefits from both allylic and ben2ylic stabilization. 

Draw the possible products resulting from addition of 1 equivalent of HC1 to 1-phenyl-1,3-butadiene. Which would you expect to predominate, and why ... 

This preparation is based on a procedure published by the submitters. 9-Phenylphenanthrene has been prepared previously by the reaction of phenyllithium with 9-chlorophelianthrene, by the high-temperature dehydrogenation with palladimn on charcoal of the Diels-Alder dimer of 1-phenyl-1,3-butadiene, and by the acid-catalyzed cyclization of the alcohol formed from the reaction of 2-biphenylylmagnesium iodide and 2-phenoxy-acetophenone. ... 

A single chloro compound, trans-1 -phenyl-3-chloro-1 -butene (7), is formed in hydrochlorination of isomeric 1-phenyl-1,3-butadienes in AcOH135 (Scheme 6.2). The observation is interpreted by the formation of different isomeric allylic carbo-cations (6c and 6t). Rapid rotation of 6c to 6t before captured by the chloride ion ensures selective formation of 7. 

Properties of Diastereomers In contrast to enantiomeric pairs, the correpond-ing spatial distances in diastereomeric pairs are not all identical. For example, errand trans-1,2-difluoroethene (Figure 1.2.4), differ in their F-F and H-H distances. This results into different energy contents and different properties between diastereomeric molecules. The difference in properties of diastereomers is illustrated with cis- and trans-1-phenyl-1,3-butadiene, which show markedly different physicochemical properties [12] (Figure 1.2.5). Further investigation of stereochemical isomers is beyond the scope of this book, and discussion in subsequent chapters is limited to constitutional isomers. 

Figure 1.2.5 Chemical structures of cis- and trans-1-phenyl-1,3-butadiene and their normal melting point, Tm, specific gravity, df, and the refractive index, nf.

The addition of HBr to 2-methyl-l,3-pentadiene, 1-bromo-1,3-butadiene, 1-phenyl-1,3-butadiene and 2,4-hexadiene produces 2,4-dibromo-2-methylpentane, 1,3-dibromo-l-butene, 3-bromo-l-phenyl-1-... 

If the reaction is allowed to become warm, substantial protodesilylation of the product takes place to give 3-methyl-1 -phenyl-1,3-butadiene. The aqueous workup should be carried out rapidly to minimize this side reaction. The use of hydrochloric acid has particular advantage since all of the salts dissolve facilitating the extractions. 

Gas chromatographic analysis (0.53-mm id x 10 m poly (dimethyl silicone) fused silica column, temperature programmed from 140°C to 220°C) indicates that this product is 98% pure, with <1% 3-methyl-1-phenyl-1,3-butadiene and 1-2% of a less volatile, unidentified component. The checkers could obtain a very pure product by normal vacuum distillation. They found the impurities to be higher boiling compounds. 

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]. 

Dioximato-cobalt(II) catalysts are unusual in their ability to catalyze cyclopropanation reactions that occur with conjugated olefins (e.g., styrene, 1,3-butadiene, and 1-phenyl-1,3-butadiene) and, also, certain a, 3-unsaturated esters (e.g., methyl a-phenylacrylate, Eq. 5.13), but not with simple olefins and vinyl ethers. In this regard they do not behave like metal carbenes formed with Cu or Rh catalysts that are characteristically electrophilic in their reactions towards alkenes (vinyl ethers > dienes > simple olefins a,p-unsaturated esters) [7], and this divergence has not been adequately explained. However, despite their ability to attain high enantioselectivities in cyclopropanation reactions with ethyl diazoacetate and other diazo esters, no additional details concerning these Co(II) catalysts have been published since the initial reports by Nakamura and Otsuka. 

The ethereal solution is filtered and concentrated by distillation from a steam bath to a residual volume of 80-100 ml. Some water separates at this time, and the mixture is cooled and then dried with about 15 g. of anhydrous potassium carbonate. The concentrated solution is filtered into a 125-ml. modified Claisen flask 2 and distilled under reduced pressure in a nitrogen atmosphere into a receiver containing 0.3 g. of phenyl-/j-naphthy]amine. In this manner 52-54 g. (80-83%) of crude fraws-1-phenyl-1,3-butadiene is obtained, b.p. 81—85°/10—11 mm. 1.606-1.608, which may contain some methylstyrylcarbinol and water. This material is dried with 5 g. of anhydrous potassium carbonate, filtered, and distilled as before. The yield of trans-1 -phenyl- 1,3-butadiene is 47 9 g. (72-75%), b.p. 78-81°/8 mm. 1.607-1.608. This product is satisfactory for most purposes (Notes 4 and 5). 

In contrast to olefins, little is known on catalytic hydroboration of conjugated dienes. Suzuki and Miyaura20 described a 1,4-addition of catecholborane to acyclic 1,3-dienes, catalyzed with tetrakis(triphenylphosphine)pa]ladium(0). An interesting Markovnikov type regioselectivity was observed in the enantioselective dihydroboration of (E)-1-phenyl-1,3-butadiene with catecholborane, catalyzed by chiral rhodium complexes.21 However, the scope of these reactions is not well known, and the choice of catalysts is very limited. 

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. 

Potassium pentacyanocobaltate(II), derived form cobalt(II) chloride and KCN, catalyzes the hydrogenation of 1,3-dienes to monoalkenes. 1,3-Butadiene (22), isoprene and 1-phenyl-1,3-butadiene (23), have been converted to mixtures of the corresponding 1-butenes, fra s-2-butenes and cw-2-butenes. The product distribution depends highly on reaction conditions such as the cyaniderCo ratio, the concentra-... 

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... 

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