S-p-Methoxybenzyl group

Strong acidolytic conditions were precluded by the presence of an N-Boc group and an activated secondary benzylic alcohol in a synthesis of the Ecteinasddin fragment depicted in Scheme 5.7. Hence, the S-p-methoxybenzyl group was excised with mercury(II) trifluoroacetate in acetic acid and the liberated thiol then cydised onto a benzylic centre under the aegis of trifiuoroacetic acid.20 21... 

During a synthesis of the antibiotic Micacocidin, a p-methoxybenzyl group was used to protect the thiol function in intermediate 8.1 [Scheme 5.8). The S-p-methoxybenzyl group was cleaved in two steps by first reacting 8.1 with 3-nitro-2-pyridinesulfenyl chloride (8.2) to give the disulflde intermediate 83 which was then treated with tributylphosphine in aqueous acetone to afford the thiol 8.4 in 69% overall yield for the two steps. ... 

Of course, it is possible to decrease the stability of the S-benzyl group toward acids by substitution with electron-releasing groups. Thus, in the S-p-methoxybenzyl group the benzyl cation is sufficiently stabilized to allow cleavage of the S —C bond with liquid hydrogen fluoride under fairly mild conditions while the S-2,4,6-trimethylbenzyl group can be removed with trifluoromethanesulfonic acid in trifluoroacetic acid in the persence of w-cresol. 

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See also in sourсe #XX -- [ ]

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