Download full text in PDF Opens in a new window. Article suggestions will be shown in a dialog on return to ScienceDirect. ... Please enable JavaScript to use all the features on this page. ... The potential use of β-trimethylsilylethoxymethyl (SEM) est??? for temporary carboxyl blocking is illustrated in a preparation of the title compound. ... Bayer AG US Pat. 3,813,432, and reference 1 above. Crude 6a is best obtained by continuous extraction, and purified by sublimation ...