Para-Methoxybenzyl ether

Hydrogenolysis of para-methoxybenzyl ether was made on 10% Pd/C in EtOH under a hydrogen atmosphere. 

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). 

In terms of electronic tuning, it has been mentioned already that electron-donating phenyl substituents confer increased lability towards oxidizing agents, and para-methoxybenzyl (PMB) ethers—introduced by methods analogous to those used for the benzyl group—are routinely employed because they can be removed highly... 

Procedure, The alkyl trichloroacetimidate can be prepared as follows. To a stirred suspension of sodium hydride (0.50 g, 21.0 mmol) in anhydrous diethyl ether (20 ml) add dropwise via cannula a solution of para-methoxybenzyl alcohol (29.0 g, 210 mmol) in diethyl ether (30 ml). After the solids have dissolved, cool the reaction vessel in an ice-salt bath and add trichloroacetonitrile (20.0 ml, 200 mmol) over a period of 15 min, then allow the reaction mixture to warm to room temperature. After 1 h concentrate the solution in vacuo to afford a syrup, then add pentane (20 ml) containing anhydrous methanol (0.8 ml) and stir vigorously. Filter off the precipitate and wash with pentane (2 X 20 ml) concentrate the filtrate and washings in vacuo to yield the alkyl trichloroacetimidate. 

Alcohol 51 on oxidation with 2-iodylbenzoic acid (IBX) followed by Barbier allylation and silylation gave diene 52. Deprotection of para-methoxybenzyl (PMB) group in 52 furnished the alcohol 53. Similarly, the known allyhc alcohol 54 was reacted with MOM Cl (methyl chloromethyl ether) to afford ether 55, which on desi-lylation and oxidation with TEMPO/BIAB (2,2,6,6-tetramethylpiperidinyloxy)/(bis-acetoxyiodobenzene) gave the acid 56 (Scheme 6.11). 

---