Hydrazino groups, protection

The first bis(hydrazino)silanes were obtained in the early 1960s.49-51 They contain organic groups such as Me or Ph bound to the nitrogen and silicon atoms, which protect the sensitive hydrazine unit. The bis (hydrazino)silanes were obtained in the reaction of diorganodichlorosi-lanes with the organo derivatives of hydrazine [Eq. (25)]. 

In one case, the benzhydryl group was used to protect the hydrazino... 

Thiazolin-4-one derivative 29 in hydrazino-hydrazono tautomeric equilibrium is synthesized by cyclization of l,2-diaza-l,3-butadiene 27 with aryl thioamide 28. Subsequent hydrolytic removal of the NH-Boc-hydrazo protecting group provided 5-acetyl-4-hydroxythiazole derivative 30a, which undergoes a-bromination to give a-bromomethyl ketone 30b. This bromide is used to prepare polyfunctionalized 4,5 -bithiazol-4 -ol derivatives via the Hantzsch thiazole synthesis <04SL2681>. 

The group ofTsogoeva discovered that BINOL-phosphate catalyst 93 can promote the enantioselective addition of TMSCN to aliphatic hydrazones 92 (Table 30.12) [50]. The so-formed a-hydrazino nitriles 95 can be readily transformed via acidic hydrolysis into biologically and synthetically important a-hydrazino acids. In general, N-p-N02-benzoyl-protected ahphatic hydrazones 92 could be converted in good enantioselectivities (71-93% ee). The yields showed inconsistency, but... 

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