Sulfide contraction procedure

Acidic cleavage of the /ert-butyoxycarbonyl group, which has served to keep the enamine double bond of rac-88 in the exocyclic position, completes the synthesis of isobacteriochlorin 93. A very similar concept has made it possible to synthesize a symmetric isobacteriochlorin <90AG(E)43> and in a modified synthetic approach the isobacteriochlorin 93 was obtained by coupling the AB- and CD-building blocks by a sulfide contraction procedure <81HCA1431>. 

Oxo-A/D-seco-corrin complexes (84) (Scheme 16) can also be synthesized by way of the new sulfide contraction procedure,and irradiation provides... 

In the case of the AB-component sulfide contraction was followed by base induced elimination of the cyano function and iodination to give 101, whereas transformation of the lactam into the thiolactam function formed 103. The sulfide contraction procedure was once again applied to couple the dimeric moieties under the influence of Ni(C104)2 as a template, followed by decomplexation, recomplexation with Zinc(II) and base induced decyanodation to yield the linear tetracyclic lactam (104). Upon treatment with MeOTf, the precorphin (104) underwent an... 

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. 

The synthesis of thiiranes with subsequent elimination of sulfur is an important procedure for the creation of C=C bonds, especially for sterically crowded systems (47,48), in analogy to the Eschenmoser-sulfide-contraction reaction (116). The spontaneous elimination of sulfur was observed in the rhodium-catalyzed reaction of diazo compound 62, which gave rise to the formation of cyclopentenone derivative 63 (117) (Scheme 5.24). A synthesis of indolizomycin was published by Danishefsky and co-workers (118) and involved a similar annulation step. In this case, however, the desulfurization reaction was achieved by treatment with Raney Ni. 

---