Lactones fonnation

No 0-allylation is observed in formation of the six-membered ring compound 79 by intramolecular allylation of the /3-keto ester 78(15,57]. Intramolecular allylation is useful for lactone fonnation. On the other hand, exclusive formation of the eight-membered ring lactone 81 from 80 may be in part derived from the preference for the nucleophile to attack the less substituted terminus of the allyl system[58]. 

Upon fonnation of intermediate LI, conjugate addition to a chalcone and subsequent proton transfer is proposed to lead to enolate LIII (Scheme 37). An intramolecular aldol addition provides activated carboxylate LIV in which alkoxide acylation regenerates the catalyst and delivers p-lactone LVI which, upon decarboxylation, gives rise to a trisubstituted cyclopentene. 

Amine 39, prepared by catalytic reduction, is separated from the catalyst by filtration through Cclite, and the resulting methanolic solution is treated with sodium methoxide. Under these basic conditions the mesylate is replaced by an amine in an SN2 reaction and the lactone is also opened with fonnation of the thermodynamically more stable lactam 11. 

A common procedure in C-C-bond formation is the aldol addition of enolates derived from carboxylic acid derivatives with aldehydes to provide the anion of the (3-hydroxy carboxylic acid derivative. If one starts with an activated add derivative, the fonnation of a (3-lactone can follow. This procedure has been used by the group of Taylor [137] for the first synthesis of the l-oxo-2-oxa-5-azaspiro[3.4]octane framework. Schick and coworkers have utilized the method for their assembly of key intermediates for the preparation of enzyme inhibitors of the tetrahydrolipstatin and tetrahydroesterastin type [138], Romo and coworkers used a Mukaiyama aldol/lac-tonization sequence as a concise and direct route to (3-lactones of type 2-253, starting from different aldehydes 2-251 and readily available thiopyridylsilylketenes 2-252 (Scheme 2.60) [139],... 

It is interesting that the 8-decalactone is formed by an entirely different biotrans-fonnation. This lactone is formed by the miCTobial reduction of an a,P-unsaturated lactone found in Massoia bark oil. Massoia bark oil contains about 80% 2-decen-5-ohde, 1% 2-dodecen-5-olide and 6% benzyl benzoate. Several microorganisms... 

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