Conjugate addition reactions Camphor

Tetrakis(triphenylphosphine)-palladium(O), 289 Conjugate addition reactions (IS, 2S)-2-Amino-3-methoxy-1 -phenyl-1-propanol, 17 Camphor, 61... 

The asymmetric conjugate addition of diethylzinc with chalcone was also catalyzed by nickel and cobalt complex (Eq. (12.31)) [71]. A catalytic process was achieved by using a combination of 17 mol% of an aminoalcohol 34 and nickel acetylacetonate in the reaction of diethylzinc and chalcone to provide the product in 90% ee [72, 73]. Proline-derived chiral diamine 35 was also effective, giving 82% ee [74]. Camphor-derived tridentate aminoalcohol 36 also catalyzes the conjugate addition reaction of diethylzinc in the presence of nickel acetylacetonate to afford the product in 83% ee [75]. Similarly, the ligand 37-cobalt acetylacetonate complex catalyzes the reaction to afford the product in 83% ee [76]. 

The camphor-derived tridentate amino alcohol 32 (Scheme 17) also catalyzes the conjugate addition reaction of diethylzinc in the presence of nickel acetylac-etonate to afford the product in 83% ee [75]. Similarly the Hgand 33-cobalt acety-lacetonate complex catalyzes the reaction to afford the product in 83% ee [76]. 

Synthesis of Chiral Auxiliaries. Their availability and crystalline nature has made camphor derivatives the precursors of choice for the design and synthesis of chiral auxiliaries. 10-Camphorsulfonyl chloride is the starting material for the synthesis of chiral auxiliaries (9)-(12) (eq 2). Sulfonamides (9) and (10) have been used as chiral auxiliaries in a number of reactions, e.g. the Lewis acid-catalyzed Diels-Alder reaction, the [3 + 2] cycloaddition of a nitrile oxide to an acrylate, and the stereoselective conjugate addition reaction of organocopper reagents to ci ,)3-unsaturated esters. ... 

Cul, methyllithium, and a camphor-derived /3-amino alcohol (239). Reaction of methylmagnesium iodide and benzylideneacetone in the presence of a small amount of a chiral Cu(I) thiolate complex gives the conjugate addition product in 57% ee (240). 

Optically pure sultams have been used by Oppolzer as chiral auxiliaries in various asymmetric transformations, including Diels-Alder reaction, aldoliza-tion, conjugate addition, his-hydroxylation, and catalytic hydrogenation [42,43]. In the literature, the most commonly used chiral sultam is derived from camphor (Oppolzer s sultam). The ready access to 80 and other chiral sultams from the Diels-Alder cycloadducts could further expand the scope of their use as chiral auxiliaries in asymmetric synthesis. 

Other auxiliaries are also used, and the choice of auxiliary may depend not only on the selectivity of the reaction under investigation but also on the physical properties of the products. The camphor-based auxiliary of Oppolzer is reputed to confer crystallinity on its derivatives, while the pseudoephedrine auxiliary of Myers is cheap, readily available, and very easy to introduce. More bulky auxiliaries such as 8-phenylmenthol work well where control over long-range interactions, such as conjugate additions, are required. 

Parameters such as, synthesis medium (HCl, camphor sulfonic add (CSA) or dodecylbenzene sulfonic acid (DBSA)), molar ratio aniline/oxidant, method for oxidant addition, temperature, polymerization duration, dedoping conditions will have effects on polymer properties in terms of yield, chain length, effective conjugation, defects rate, and electrical properties. Temperature was kept to 0 C, -30 C or -40 C and reactions were stopped after various durations in order to control the molecular weight of samples. Polymerization durations were varied from 1 hour to 5 days and depended on the reaction temperature. The inherent viscosities of the polyanilines (Pani) were determined at 25 °C in 0.1%w solutions in concentrated sulfuric acid (95 %), using an Ubbelohde viscometer. For instance, high viscosity samples (1.4 dl/g) were obtained after 3 days at -40 °C vsMe low viscosity samples (0.6 dl/g) were obtained after 1 hour at 0 A relationship was found between polymerization duration and inherent viscosity for polymers synthesized at low temperature (- 40 °C). Inherent viscosity increases from 0.6 to 1.4 when duration of polymerization increases from one to five days. In the case of synthesis at 0°C no correlation was obtained between duration of polymerization and inherent viscosity. A careful control of other parameters (synthesis medium, molar ratio aniline/oxidant, method for oxidant addition) have permitted to get samples with inlierent viscosities ranging from 0.55 to 2.1 dl/g in a reproducible way. 

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