Anhydro-1 -hydroxythiazolo

Cyclocondensation of anhydro-1 -hydroxythiazolo[3,2-a]quinazolinium hydroxides (334) with dipolarophiles (335) afforded 5-methyl-5,6-dihydro-1 //-pyrido[l, 2-n]quinazoline-l, 6-diones (337) (85JOC1666). Sometimes better yields were achieved when mesoionic compounds (334) were prepared in situ from S-(quinazolin-2-yl)thioglycolic acids (333, R = Ph) with acetic anhydride or DCC in the presence of the dipolarophiles (335). Cycloadducts 336 (R = H, Ph, R1 = R2 = CN) could be characterized in the case of fumaronitrile by IR and 1H NMR spectroscopy. 

Mesoionic compounds may undergo 1,3-dipolar cycloaddition reactions. Thus anhydro-1 -hydroxythiazolo[3,2-a]guinolinium hydroxide (396) is a substrate for the reaction with DMAD. The formation of the pyrrolo[l,2-a]quinoline (397) from this reaction involves COS elimination from the initial adduct. Ethyl propiolate also reacts in the same fashion. The orientation in the cycloadduct can be arrived at from the ylide form (396a). With fumaronitrile, however, the fused pyridinone (398) is formed by loss of sulfur from the primary cycloadduct (78JOC2700). 

Pyridazines with an appropriate side chain attached to the sulfur atom at position 3 can be transformed into bicyclic systems. For example, pyridazinyl /3-ketoalkyl sulfides are cyclodehydrated in sulfuric acid to give thiazolopyridazinium salts, and 3-carboxymethyl-thiopyridazines are transformed by acetic anhydride in pyridine into 3-hydroxythiazolo[3,2-6]pyridazinium anhydro salts (Scheme 52). 

The reactions of anhydro 2-aryl-3-hydroxythiazolo[2,3-a]phthalizinium hydroxides (171) with methyl propiolate (87EUP226196 88EUP294599), dimethyl acetylenedicarboxylate (85JOC1677), or fumaronitrile (85JOC1677) gave 4//-pyrido[2,l-a]phthalazin-4-ones (173) via cycloadducts 171. When methyl vinyl ketone was reacted with 171 (R = H), in addition to 9% of 4//-pyrido[2,l-a]phthalazin-4-one (173, R = H, R = COMe), a cycloadduct was also isolated (85JOC1677). 

Berninamycinic acid (anhydro-3,8-dicarboxy-6-hydroxythiazolo[2,3-/]-[l,6]naphthyridin-4-ium hydroxide) (76JA299)... 

Berninamycinic acid is one of the products from acid hydrolysis of the cyclic peptide antibiotic berninamycin A, which is a potent inhibitor of bacterial protein synthesis. Berninamycinic acid has been assigned the structure (524), anhydro-3,8-dicarboxy-6-hydroxythiazolo[2,3-/][l,6]naphthyridin-4-ium hydroxide. The 6-hydroxy group arises during hydrolysis from a peptide-bonded amino group (77JA1645). 

Acid hydrolysis of bovine liver yields (R)-anhydro-3-carboxy-2,3-dihydro-8-hydroxythiazolo[3,2-a]pyridinium hydroxide (479 R1 = H, R3 = Me). This last is formed from the amino acid L-cysteine and carbohydrates present (81H(15)1349). 

Pyrido[l,2-c]quinazolin-8-ones (215) were obtained from the cycloadducts (214) of anhydro 3-hydroxythiazolo[3,2-c]quinazolin-4-ium hydroxides (213) and alkynic (dimethyl acetylenedicarboxylate and ethyl propio-late) and alkenic dipolarophiles (fumaronitrile and methyl vinyl ketone) by extrusion of S or H2S (85JOC1666). A better yield could sometimes be... 

Another mesoionic system used as dipolarophile was a cyclic system of anhydro-2-hydroxythiazolo[l,3-b]benzothiazol hydroxide 177. This compound was prepared in situ from thionobenzothiazole 176 by reaction with acetic anhydride. The subsequent reaction with hexafluorobut-2-yne led to the tricyclic 3,4-bis(trifluoromelhyl) pyrrole 178 [69]. 

Potts KT, Choudhury DR (1978) Mesoionic compounds. 43. Ring annulation utilizing the isomeric anhydro-2- and 3-hydroxythiazolo[2,3-b]benzothiazolium hydroxide mesoionic... 

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