5.6- DIHYDRO-2ff-PYRAN-2-ONE

Chiral phosphonous acid diester induces the kinetic resolution of racemic a-substituted y-unsaturated carboxylic acids through asymmetric protolac-tonization (Scheme 53) (130L2838). Dinamic kinetic resolution with Candida antartica lipase B and the ruthenium catalyst [RuCl(CO)2(T -C5Ph5)] of several homoallylic alcohols is applied in the key step to the synthesis of enantiomericaUy pure 5,6-dihydro-2ff-pyran-2-ones ( [13CEJ13859]). 

Dihydro-2f/-pyran-2-one has been prepared by reductive cycliza-tion of 5-hydroxy-2-pentynoic acid [2-Pentynoic acid, 5-hydroxy-], which is obtained in two steps from acetylene [Ethyne] and ethylene oxide [Oxirane] 3 and by the reaction of dihydropyran [277-Pyran, 3,4-dihydro-] with singlet oxygen [Oxygen, singlet].4,5 2ff-Pyran-2-one has been prepared by pyrolysis of heavy metal salts of coumalic acid [2//-Pyran-5-carboxylic acid, 2-oxo-],8 by pyrolysis of a-pyrone-6-carboxylic acid [211 - Pyran-6-carboxyl ic acid, 2-oxo-] over copper,7 and by pyrolysis of coumalic acid over copper (66-70% yield).8... 

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