Oxidation bicyclic dihydropyran

A domino reaction involving two consecutive oxidations followed by a hetero Diels-Alder reaction led to the formation of bicyclic dihydropyran 14 in 74% yield (Scheme 9.3). In this process, developed by Koo et al. [5] using Mn(OAc)3 and Cu(OAc)2, the P-ketoester 11 having a geranyl group at the a-position is converted into the a-ketoester 12, which undergoes further oxidation to form the tertiary alcohol 13 and is followed by an intramolecular hetero Diels-Alder reaction to provide the desired bicyclic trans-fused dihydro cyclopenta[c]pyran 14. In 2012,... 

In order to cleave the bicyclic C-glycoside to the desired functionalized dihydropyran, 284 was exposed to sodium amalgam. Syn-dihydroxylation of 285 (OSO4-NMO) gave a mixture of diastereomeric tetrads, which after separation, protection-deprotection procedure and oxidation of the product C-l alcohol, using generated in situ ruthenium tetraoxide, gave the acid 254. 

The lactonization of MBH derivatives to give 3-arylidene-3,4-dihydropyran-2-one derivatives has been realized by treatment with TFAA in CH2CI2 at room temperature.As shown in Scheme 4.102, ot-arylidene-8-lactones 317 were obtained in 50 83% yields. Subsequent oxidation of 317 with PCC afforded the desired a-pyrones 318 in 51-64% yields. By application of this synthetic strategy, tricyclic compound 320, previously reported by Basavaiah and Satyanarayana, " and bicyclic compound 319 could be prepared from easily available MBH adducts. 

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