Ring opening reductive

Recently, Hoff and Blok report the reductive ring opening of 4-methyl-A-4-thiazoline-2-thione anion (80) (Scheme 39) (204) when treated with two equivalents of sodium in liquid amonia. Treatment of the prop-enethiolate (83) by 4N aqueous HCl affords 4-methylthiazole. The... 

Methylthio- and 2-ethylthio-4-methylthiazoles undergo reductive ring opening when treated by sodium in liquid ammonia (204). The first step of this reaction consists of the formation of the A-4-thiazoline anion (80). The next steps are analogous to those given for 80a to 83. 

WASSERMANN BORMANN Maciocydiclactamsynttwsis Ring expansion sequence of lactams by reaction with cyclic Iminoethers followed by reductive ring opening to a macrocyclic lactam. 

Treatment of oc-cyclopropyl ketones with lithium in a mixture of N,N-d2 propylamine and hexamethylphosphortriamide is a recently reported method for deuterium labeling via reductive ring opening. This reaction provides y-labeled ketones in good yield (70-100%) and isotopic purity (85-93%). 

Reductive ring opening of epoxides in radical reactions in presence of titanocenes as electron transfer catalysts 98SL801. 

Reductive ring opening of the [i-lactam 10 (X = O), obtained by [2 + 2] cycloaddition of chloro-sulfonyl isocyanate and tetraphenylcyclopentadiene followed by treatment with /7-cresol, with sodium hydride in anhydrous tetrahydrofuran yields 3,5,6,7-tetraphenyl-2//-azepin-2-one (11, X = O).41 Surprisingly, similar treatment of the reduced /Mactam 10 (X = H2) is reported to yield 3,5,6,7-letraphenyl-2//-azepine (11, X = H2), the first monocyclic 277-azepine to be isolated and characterized. Physical data for this compound, however, are inconclusive and attempts to reproduce this synthesis have failed.291... 

Reductive ring-opening reaction of aziridine ester constitutes a convenient access to amino acids a typical example is given in Scheme 27 [37]. 

Hydroaluiriination of Functional Croups 61 Tab. 2-3 Reductive ring opening of unsymmetric oxabicyclic substrates ... 

The presence of a free hydroxyl group is not a requirement for high selectivity, as demonstrated by the reductive ring opening reaction of the methyl and TBDMS... 

Hydroalumination of Functional Croups 65 Tab. 2-5 Enantioselective reductive ring opening of oxabicyclic subrates... 

The asymmetric reductive ring opening of oxabenzonorbomene 53 was applied as a key step in the total synthesis of serotonin re-uptake inhibitor sertraline [77, 80]. 

To date, synthetically useful enantioselective hydroalumination is limited to the asymmetric reductive ring-opening reaction of bicycHc ethers. In spite of the fact that further studies are necessary to get a detailed understanding of the reaction mechanism, this reaction provides a new route to various cycloalkenol derivatives, which are useful intermediates in the preparation of biologically active compounds. 

It is remarkable that more than a century after the discovery of tetrazoliums, they continue to have wide applications. In particular, the reductive ring opening reaction leading to formazans continues to receive a lot of attention. In 1993, there were 316 citations to tetrazolium salts in Chemical Abstracts, 23 of which were to their reduction. Yet, the same reaction that makes them a unique class of reduction indicator leuco dyes, may be a part of a broader phenomenon. 

It would seem likely that tetrazolium salts are only one class of a wider variety of redox indicators acting through reductive ring opening, and that many more examples will be discovered in the future that may open some new directions to the chemistry of tetrazolium salts. 

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