Sulfide contraction method

The synthetic pathways leading to tetradehydrocorrins and isobacteriochlorins are very similar and it is just by fine variations of the reaction conditions that the preparation is driven towards specific tetrapyrrolic rings. The linear precursors have been synthesized using the sulfide contraction method (also indicated by other authors as sulfur extrusion ). The corrin skeleton is formed by alkaline hydrolysis of the cyano protecting group present at the 19 position and subsequent acid catalyzed coupling of pyrroles A and D, as described in Fig. 26. 

Ring B pyrrole aldehyde (78) and ring C lactam (79) form under base induced condensation and subsequent introduction of sulfur the bicyclic BC thiolactam (80). This bicyclic lactam was coupled by a modification of Eschenmoser s sulfide contraction method 58) with the monocyclic chiral D building block (81) to yield after ester cleavage and complexation with nickel (II) the tricyclic intermediate (82). After hydrogenolytic cleavage of the benzylester in (82) the crude carboxylic acid formed with the ring A pyrrole aldehyde (83) the linear tetrapyrrole... 

This procedure illustrates a broadly applicable method which is essentially that of Roth, Dubs, Gotschi, and Eschenmoser,2 for the synthesis of enolizable /1-dicarbonyl compounds. Although there are various methods for the preparation of /3-dicarbonyl systems,3 the scheme of sulfide contraction widens the spectrum of available methods. The procedure can also be utilized in the synthesis of aza and diaza analogs of /3-dicarbonyl systems. Eschenmoser2 has utilized the method to produce vinylogous amides and amidines in connection with the total synthesis of corrins and vitamin B12.4... 

The selection of the thirty procedures clearly reflects the current interest of synthetic organic chemistry. Thus seven of them illustrate uses of T1(I), T1 (III), Cu(I), and Li(I), and three examples elaborate on the process now termed phase-transfer catalysis. In addition, newly developed methods involving fragmentation, sulfide contraction, and synthetically useful free radical cyclization arc covered in five procedures. Inclusion of preparations and uses of five theoretically interesting compounds demonstrates the rapid expansion of this particular area in recent years and will render these compounds more readily and consistently available. 

Sakurai, O., Ogiku, T, Takahashi, M., Horikawa, H., and Iwasaki, T. 1994. A new synthetic method of Ib-methylcarbapenems utilizing the eschenmoser sulfide contraction. Tetrahedron Lett 25, 2187-2190. 

The Eschenmoser reaction was applied a second time as one of the methods to introduce the -butyl appendage. The alkylated a-amino ester (97) was oxidized to the monosubstituted thiolactam (98), and introduction of the butyl side chain, via sulfide contraction as described above, yielded a mixture of vinylogous carbamates (99). Treatment of the carbamates (99) under transfer hydrogenolysis conditions yielded the optically pure dialkylpyrroline (100), another component of the ant trail pheromone. Subsequent reduction of the pyrroline with platinum afforded the optically pure ds-2,5-dialkyl-substituted pyrrolidine (101). Other pyrrolidine-containing alkaloids have been prepared by similar approaches involving the Eschenmoser reaction. ... 

A method for C-C coupling, which is based on closing a thiirane ring and opening it by desulfurization, is known as sulfide contraction after Eschenmoser, e.g. ... 

Minehan TG, Kishi Y (1997) Extension of the Eschenmoser Sulfide Contraction/ Iminoester Cyclization Method to the Synthesis of Tolyporphin Chromophore. Tetrahedron Lett 38 6811... 

Roth, M. Dubs, P. Goetschi, E. Eschenmoser, A. Synthetic Methods. 1. Sulfide Contraction via Alkylative Coupling Method for Preparation of )3-Dicarbonyl Derivatives Helv. Chim. Acta 1971, 54, 710-734. 

Symmetrical dialkyl 1,2,4-trithiolanes can be prepared by reaction of di-a-chloroalkyl sulfides (145) with Na2S or ring contraction of the tetrathiepane (146) using nucleophilic reagents such as triphenylphosphine or cyanide (Scheme 41). Both methods give cisjtrans mixtures and most examples of the latter involve R = aryl <88CL1517>. 

Contracts for acetylene-grade carbide are usually based on size and gas yidd specification, and indude penalties for carbide that fails to meet specified gas yidd. The sizes generally available in the trade are based on established U.S. Government specifications. In general gas yidds range from 280—300 L/kg and depend on the screen size of the carbide. The most important standard is the method of expressing gas yidd, which in the United States is at 15°C and 101 kPa (1 atm). Gas impurities are typically 0.05% by volume phosphine, 0.15% by volume hydrogen sulfide, and 0.001% arsine. 

The latter method via cyclization and subsequent ring contraction at one or several centres in most cases makes use of cyclizations to sulfides [3]. These cyclizations follow Sn mechanisms and are easy to carry out giving high yields of the cyclic sulfides, which are easily isolable [6, 7], For the ring contraction step, in this case a desulfurization step, a variety of methods is at hand ... 

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