Ziegler schemes

At this point, it is important to notice that in general, the sum of the contributions do not match exactly AE as higher order terms are present. The difference between the sum of contributions and AE is denoted 8E. Concerning the variational schemes, SE is generally small in the CSOV (or RVS) approach thanks to the antisymmetry conservation and not present in the Ziegler scheme as the Eoi term is taking into account a fully relaxed wavefunction. It is not the case for the KM scheme which... 

Lounasmaa used the reaction in a synthesis of (Z)-geissoschizol [55] based on early precedence provided by Ziegler (Scheme 7.27) [56]. Stereoselective rearrangement of 74 gave unsaturated amide 75 featuring the trisubstituted (Z)-double bond of the natural product. Hydrolysis of the dimethyl amide required forcing conditions and was immediately followed by Fischer esterification. 

Table 7 Eneigy decomposition analysis according to the Morokuma Ziegler scheme...

The first example of homogeneous transition metal catalysis in an ionic liquid was the platinum-catalyzed hydroformylation of ethene in tetraethylammonium trichlorostannate (mp. 78 °C), described by Parshall in 1972 (Scheme 5.2-1, a)) [1]. In 1987, Knifton reported the ruthenium- and cobalt-catalyzed hydroformylation of internal and terminal alkenes in molten [Bu4P]Br, a salt that falls under the now accepted definition for an ionic liquid (see Scheme 5.2-1, b)) [2]. The first applications of room-temperature ionic liquids in homogeneous transition metal catalysis were described in 1990 by Chauvin et al. and by Wilkes et ak. Wilkes et al. used weekly acidic chloroaluminate melts and studied ethylene polymerization in them with Ziegler-Natta catalysts (Scheme 5.2-1, c)) [3]. Chauvin s group dissolved nickel catalysts in weakly acidic chloroaluminate melts and investigated the resulting ionic catalyst solutions for the dimerization of propene (Scheme 5.2-1, d)) [4]. 

The biochemical mechanism of bacterial luminescence has been studied in detail and reviewed by several authors (Hastings and Nealson, 1977 Ziegler and Baldwin, 1981 Lee et al., 1991 Baldwin and Ziegler, 1992 Tu and Mager, 1995). Bacterial luciferase catalyzes the oxidation of a long-chain aldehyde and FMNH2 with molecular oxygen, thus the enzyme can be viewed as a mixed function oxidase. The main steps of the luciferase-catalyzed luminescence are shown in Fig. 2.1. Many details of this scheme have been experimentally confirmed. 

The oligomerization of the ethylene proceeds as a ligand reaction in the coordination sphere of the catalyst complex, as the following reaction scheme shows. The reaction course corresponds with the Ziegler process for ethylene polymerization. 

Protonation of the TMM complexes with [PhNMe2H][B(C6Fs)4] in chlorobenzene at —10 °C provided cationic methallyl complexes which are thermally robust in solution at elevated temperatures as determined by NMR spectroscopy. In contrast, addition of BfCgFsls to the neutral TMM precursors provided zwitterionic allyl complexes (Scheme 98). Surprisingly, it was found that neither the cationic nor the zwitterionic complexes are active initiators for the Ziegler-Natta polymerization of ethylene and a-olefins. °°... 

Scheme 6 Scheme of the initiation mechanism in ethylene polymerization according to a Ziegler-Natta-like behavior... 

IFIGU RE 22.11 The catalytic scheme for polymerization by the Ziegler-Natta process. 

Ziegler and coworkers prearranged a glycoside by employing a succinyl tether between C-6 of a mannosyl donor and C-3 of glucosyl acceptor [151,152]. They found that the nature of the glycosyl acceptor and the length of the tether affected the anomeric selectivity of the intramolecular mannosylation (Scheme 4.4d) [153]. 

Fig. 1.10. Scheme of the (SHOP) utilizing a non-Ziegler catalyst system. 

In Ziegler and Kloek s synthesis of ( )-steviol methyl ester, irradiation of hydrin-denal 17 and 1,2-propadiene (1) afforded the photocycloadduct 18 in 45% yield as a 14 1 mixture of diastereomers (Scheme 19.4) [6]. The major cycloadduct was subsequently converted to ( )-steviol methyl ester via a reduction of the aldehyde, followed by mesylation of the resulting alcohol and treatment with aqueous acetone in 2,6-lutidine. Unfortunately, steviol methyl ester (19) was obtained in only 3% yield. 

An enantioselective synthesis of the Ziegler intermediate 107 of forskolin (108) has been achieved using an intramolecular allenic Diels-Alder reaction (Scheme 19.20) [24], Treatment of propargyl ether 104 with potassium tert-butoxide in tert-butanol affords 106, presumably through the intermediate allene 105. Compound 106 was obtained as a single stereoisomer. 

In the particular case in which the carbonyl group belongs to a carboxylic acid derivative, such as an ester (17) or an amide (18) (or other functional groups which may be converted into it by a FGI), then they may be disconnected according to the "orthoacetate-modification" of the retro-Claisen rearrangement (Schemes 7.7 and 7.8) developed mainly by Eschenmoser [7] and Ziegler [8], independently, in the synthesis of alkaloids, and Johnson in a very simple and yet highly stereoselective synthesis of squalene [9]. 

Most probably, the last stage in the synthesis of 2-amino-4H-pyrans involves base-catalyzed nucleophilic addition of the enolic oxygen to a C=N group, which can be regarded as a hetero-Thorpe-Ziegler reaction (Scheme 21). 

Multicomponent reactions of this type, in the concepts of Tietze, who introduced the term domino reactions (96CRV115), can also be regarded as domino reactions of the type Knoevenagel-Michael-ljef-ero-Thorpe-Ziegler in accordance with the probable mechanistic scheme (Scheme 32). 

Two similar syntheses have been reported by Ziegler and co-workers (487) and Kametani et al. (488,489). Reaction of N-methylisatic anhydride (584) with thioacetamide afforded glomerin (60) in 58% yield (487). The other synthetic route is as follows The sulfinamide (585), prepared from N-methylanthranilic anhydride and thionyl chloride, was treated with acetamide and propionamide to afford glomerin (60) and homoglomerin (61), respectively (Scheme 72) (488,489). 

---