Sulfur ring closures with

Further examples of the Knorr reaction for the synthesis of 3-hydroxy-4,7-phenanthrolines are reported. A modification of the original synthesis239 of 3-hydroxy-1-methyl-4,7-phenanthroline involves isolation of the intermediate acetoacetanilide followed by ring closure with sulfuric acid.232 10-Amino-3-hydroxy-l-methyl-4,7-phenanthroline was obtained similarly from 4-amino-6-acetoacetamidoquinoline. Several 2-substituted l,3-dihydroxy-4,7-phenanthrolines were obtained likewise from diethyl alkylmalonates.101... 

Procedure V. Ring Closure with Sulfuric Acid.198 For the conversion of Y-arylbutyric acids into cyclic ketones, the finely powdered acid (1 part) is added gradually with stirring to a mixture of concentrated sulfuric acid (3 volumes) and water (1 volume). After one hour s heating on the water bath the colored solution is cooled, diluted with water by pouring onto ice, and extracted with ether. The extract is washed with water, which removes traces of colored sulfonation product, then with dilute aqueous ammonia, and dried over anhydrous potassium carbonate the solvent is removed, the residue distilled under reduced pressure, and the distillate crystallized from a suitable solvent. 

The original method (A) involves conversion of the bis-tosylate to the cyclic diselenide followed by reduction of the Se-Se bond and ring closure with sulfur monochloride (eq 1). This method was recently improved in both yield and simplicity using a sulfur insertion methodology (path B, eq 1). ... 

Without additional reagents Ring closures with sulfur 2-Aminothiazole ring from enamines... 

Ring closure with sulfur monoxide Cyclic sulfoxides from 1,3-dienes... 

Cl Vat Red 10 is prepared by condensation of l-nitroanthraquinone-2-carboxyhc acid chloride with 2-amino-3-hydroxyanthraquinone followed by ring closure in sulfuric acid and subsequent replacement of the nitro group with aqueous ammonia. 

Azide, sulfonium ylides and (V-aminopyridinium ylides are also known to add to the 2-position of substituted thiopyrylium compounds (presumably via reversible addi-tion/elimination sequences, as for methoxide) and cause ring opening followed by ring closure with loss of sulfur. Scheme 24 shows these conversions (80NKK604). 

Condensation of acetoacetic ester with a-bromocyclopentanone, followed by ring closure with cold sulfuric acid, gave 2-methyl-3-carboxy-4,5-trimethylenefuran in 41% yield53 ... 

Formation of a cyanoformamidine by treatment of a symmetrical diphenylthiourea with potassium cyanide in alcohol containing lead carbonate, reduction with ammonium sulfide, and ring closure with concentrated sulfuric acid to isatin-2-anil also formed smoothly by ring closure of the cyanoformamidine with aluminum chloride in benzene or carbon disulfide. 

Pseudoheliotridane (XXXVIa) has been prepared by Cervinka (130) in a novel manner from l-methyl-2-ethyl-J2.pyrroline (XXXVII) by reaction with ethyl bromoacetate and heating of the resulting product with potassium formate and sulfuric acid to give erythro -( )-3-(IV-methyl-2-pyrrolidyl)but3Tate (XXXVIII). Reduction with lithium aluminum hydride and ring closure with hydrobromic acid yielded XXXVIa. 

Ring closure with a sulfided catalyst has been described by Hummer and Taylor (23). When molybdenum dioxide supported on alumina was treated with sulfur compounds it was found to retain some of the sulfur and to gain in activity as a catalyst. It was, however, quite distinct in its properties from a normal M0S2 catalyst which has a strong cracking action. 

Sulfuric acid acetic acid Ring closure with azo compds. 

Mercuric oxide sulfuric acid Ring closure with acetylene derivs. 0-Heterocydics... 

Sulfuric acid Double ring closure with double position shift of substituents of isocycles... 

The thiazolyl-2-thioglycollic acid (119) undergoes intramolecular ring closure to give mesoionic compound 120 under treatment with acetic anhydride and triethylamine (Scheme 60) (192). The parent acid (119) can be recovered from 120 by hydration with hot 50% aqueous sulfuric add. Compound 120 affords monohydrate of bis(-cyclopentenothiazolyi-2-thio)acetone (121) (192). 

---