Cleavage benzyl ether protecting group

Scheme 27 Oxidative cleavage of the benzyl ether-protecting group.

Palladium on charcoal is commonly used to promote cleavage of benzyl ether protecting groups and ultrasound was successfully used to enhance the rate of hydrogenation of the nocardicin derivative (58) [247] (Scheme 121)... 

In this section, the formation and cleavage of eight protecting groups for alcohols and phenols are presented acetate acetonides for diols benzyl ether para-methoxybenzyl (PMB) ether methyl ether methoxymethylene (MOM) ether ferf-butyldiphenylsilyl (TBDPS) silyl ether and tetrahydropyran (THP). 

Preferential cleavage of benzyl ethers Protection of phenol groups as benzyl ethers... 

Several methoxy-substituted benzyl ethers have been prepared and used as protective groups. Their utility lies in the fact that they are more readily cleaved oxidatively than the unsubStituted benzyl ethers. The table below gives the relative rates of cleavage with dichlorodicyanoquinone (DDQ). ... 

The completion of the synthesis of key intermediate 2 requires only a straightforward sequence of functional group manipulations. In the presence of acetone, cupric sulfate, and camphorsulfonic acid (CSA), the lactol and secondary hydroxyl groups in 10 are simultaneously protected as an acetonide (see intermediate 9). The overall yield of 9 is 55 % from 13. Cleavage of the benzyl ether in 9 with lithium metal in liquid ammonia furnishes a diol (98% yield) which is subsequently converted to selenide 20 according to Grie-co s procedure22 (see Scheme 6a). Oxidation of the selenium atom... 

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