Isochromene carboxylates

An expedient method for the preparation of isochromene carboxylates (203) has been developed, which relies on the regioselective 1,6-addition of various nucleophiles, such as Grignard reagents, alkoxides, and cyanide, to benzopyranylidenetungsten(O) complexes (201), followed by iodine oxidation of the addition intermediates (202)254 DFT calculations have been carried out to rationalize the unusual switch in stereoselectivity, where ynone and ynoate substrates exhibit opposite stereochemical preferences in the stannylcupration.255... 

The monophosphonium salt derived from l,2-di(bromomethyl)benzene reacts with sodium carboxylates to afford high yields of the ester (190). Generation of the ylide results in spontaneous cyclization via an intramolecular Wittig reaction to the isochromene (Scheme 35) (79TL2149). 

Citrinin, also known as antimycin, or by its chemical name (3R,4S)-8-hydroxy-3,4,5-trimethyl-6-oxo-4,6-dihydro-3H-isochromene-7-carboxylic acid (12-99) can exist in two tautomeric forms. The quinoid form is normally present in neutral media and the tautomeric phenol form occurs in alkaline media. Citrinin is a secondary metabolite of fungi of the genera Aspergillus and Penidllium, especially of fungi P. dtrinum and P. verrucosum. Citrinin is the main contaminant of so-called yellow rice (see Section 12.3.1). In temperate climates it is found mainly in cereals, but data concerning its occurrence are limited. Citrinin has also been found in cheeses, sake and commercial red yeast rice supplements (see Section 9.7). 

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