The Jaworsky Reaction

It was through Jaworsky s work at Reformatsky s laboratory, that the use of the one-step Barbier reaction for the preparation of homoallylic alcohols became a reaction of fundamental importance in organic synthesis [21]. It is therefore of no surprise that this procedure is often referred to as the Jaworsky reaction . 

Jaworsky, followed by many other researchers in and outside Reformatsky s research group, applied the one-step Saytzeff-Wagner method in which zinc was replaced by magnesium  

One of the possible dangers of a one-pot execution of a reaction is that it leads to the simultaneous presence in the reaction mixture of the products and the reactants this can cause uncontrolled reactions between these reagents. 

A very obvious one in this context would be the Williamson-type ether-formation reaction which indeed was observed during a Jaworsky reaction which included allyl chloride and propanone earlier in this century [40]  

It should be mentioned here however that products of this type are seldom reported and therefore seem not to be formed in considerable quantities. The reaction of the halide with the metal and consecutive reaction of the intermediate organometallic species (see Sect. 4.4 for a discussion of the mechanism of the Barbier reaction) with the carbonyl compound seems to be fast enough to prevent this ether formation. 

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This was the start of a series of publications on one-step reactions with allylic halides-the Jaworsky reaction-which will be further discussed in Chapter Two. 

Table 2.2 presents some of the results obtained with the Jaworsky reaction in the beginning of this century and demonstrates its versatility as well as typical yields. 

In 1963, approximately fifty years after the introduction of the Jaworsky reaction, Dreyfuss made another attempt to establish the advantages of the Barbier reaction [51]. 

When it was found, very soon after the discovery of the Grignard reaction (i.e. the Grignard reagent formation reaction), that allylic organomagnesium halides were difficult to prepare, this led to the development of the Jaworsky reaction, the one-step procedure with allylic halides. Yields with this procedure are shown in this chapter to be excellent in spite of original negative reports... 

Jaworski, J. S. Looking for a contribution of the non-equilibrium solvent polarization to the activation barrier of the Sn2 reaction. J. Phys. 

The most systematic name would be the one in which the procedure is made clear to the reader such as one-pot reaction (e.g. in [30] and [31]) or one-flask reaction, in situ reaction [32], one-step reaction [33], etc. and such names are often encountered. However more often names such as modified) Wagner-Saytzejf reaction, Saytzeff reaction, Barbier-Grignard reaction [29], [34], [35] and [36], batch-method [36], Dreyfuss-Barbier reaction [37], Jaworsky reaction [38], Grignard-type reaction [39], [40], etc. are used. 

Table 2.2. Results of some Jaworsky reactions as published at the beginning of this century.

In the same period quite some criticism came on the application of the Barbier (Jaworsky) reaction [48] ... 

Except for the successes of Jaworsky in the beginning of this century and the industrial patent by Khorr some twenty years later no other promising results with the Barbier reaction were published until recently. 

The work illustrates that after some experimenting-in order to find the optimal reaction conditions-Davies and Kipping s conclusions, as well as those of Jaworsky, Knorr and Dreyfuss have to be taken serious. 

The lack of fatty acid desaturation in the form of acyl-ACP or acyl-CoA was also suggested by in vitro experiments of Lem and Stumpf (1984a), and Stapleton and Jaworski (1984b), who studied fatty acid synthesis in crude extracts from A. variabilis. Under optimal conditions for fatty acid synth is, only saturated fatty acids, 14 0, 16 0 and 18 0, were produced from [ C]acetate. Neither added 18 0-ACP nor 18 0-CoA was desaturated. All of these observations suggest that saturated acyl-thioesters are the final products in fatty acid synthesis, and that all the desaturation reactions take place after the fatty acids are esterified to the glycerol moiety of the lipids. 

Tomin VI, Tomin VI, Jaworski R (2008) Investigation of reactions from the highest excited states of molecules by fluorescent spectroscopy methods. Opt Spectros 104 40-49... 

A solvent may play a decisive role when a reaction chooses the ion radical pathway. For instance, the solvent effect on the thermodynamic contribution to the activation free energy causes an increase in the cleavage rate constant for the chloroanthracene anion radical with an increase in the solvent acceptor number. There are examples of similar solvent effects in a review by Jaworski (1998). 

Jaworski et al. [186] found that the reaction constants from the Hammett equation, in the case of the irreversible electroreduction of substituted chloro- and bromo-benzenes in a number of organic solvents, are linearly dependent on the logarithms of the solvent longitudinal relaxation times. 

Recently Jaworski and coworkers [303] have analyzed mixed solvent influence on surface intramolecular reactions. The authors tried to explain the change in the rate constant with the H2O-DMF mixed solvent composition in terms of the change in the estimated longitudinal relaxation time. A linear correlation was found between k for various H2O-DMF compositions and Tl . 

Jaworski (4) reported that growth inhibition of both plant and microbes by glyphosate could be reversed by aromatic amino acids. Further work of Amrhein and his coworkers revealed that glyphosate inhibits the shikimate pathway enzyme, 5-enolpyruvylshikimate 3-phosphate (EPSP) synthase (5). This enzyme catalyzes the reaction shown in Figure 1. Glyphosate-treated plant and bacterial cultures accumulate shikimate and/or shikimate 3-phosphate (S3P), confirming that inhibition of EPSPS is at least a part of the in vivo mechanism of action of this herbicide (6, 7). 

Despite the presence of acetyl-CoA ACP acyltransferase activity in plant fatty acid synthase preparations, acetyl-ACP does not appear to play a major role in plant fatty acid synthesis (J. Jaworski, 1993). Instead, the first condensation takes place between acetyl-CoA and malonyl-ACP. This reaction is catalyzed by P-ketoacyl-ACP synthase III, one of three ketoacyl synthases in plant systems (Fig. 2). The acetoacetyl-ACP product then undergoes the standard reduction-dehydration-reduction sequence to produce 4 0-ACP, the initial substrate of ketoacyl-ACP synthase I. KAS I is responsible for the condensations in each elongation cycle up through that producing 16 0-ACP. The third ketoacyl synthase, KAS II, is dedicated to the final plastidial elongation, that of 16 0-ACP to 18 0-ACP. 

This desaturation reaction is in many ways analogous to the desaturation of ACP-bound stearate to oleate as is known from plastids and bacteria. It was demonstrated (Jaworski and Stumpf, 1974) that this reaction was dependent on oxygen which serves as an electron acceptor and is reduced to H2O, with NADPH being used as a coreductant (see also Kikuchi and Kusaka, 1986). The reaction was mediated by an enzyme, ferredoxine NADP -oxidore-ductase (EC 1.18.1.2.). 

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