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DOI: 10.1055/sos-SD-030-00450

Kibayashi, C.; Yamazaki, N.Science of Synthesis, (200730587.

3-Methyl-2,3-dihydrobenzothiazoles 7 are conveniently prepared by S,N-acetalization of aldehydes or ketones 6 with 2-(methylamino)benzenethiol (5), which is typically used for the protection of carbonyl compounds. Generally, this method can be applied efficiently to a variety of aldehydes or ketones, but the reaction of hindered ketones such as diisopropyl ketone hardly proceeds (Scheme 2).[‌1‌] Removal of the protecting group can be performed by using silver(I) nitrate or mercury(II) chloride in aqueous acetonitrile. This reaction involving S,N-acetalization is used in a more complex sequence. For example, the reaction of homopenicillamine (8) with methyl glyoxylate (9) leads to the thiazolidine-4-acetic acid 10, which can be converted into the isopenam 11 as a precursor of isopenicillin G (Scheme 2).[‌2‌]

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(8M*,8M*)-8-(Meeeeeeeeeeeeee)-8,8-eeeeeeeeeeeeeeeeeeee-8-eeeeee Meee (88):[‌8‌]

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