## 3 Application of Complex [PtH{(PMe2O)2H}(PMe2 OH)] in the Total Synthesis of Natural Products  
Capuramycin (**5**), a nucleoside antibiotic isolated from the culture filtrate of _Streptomyces griseus_ 446-S3 [22], and its congeners are considered to be important lead molecules for the development of new drugs for _Mycobacterium tuberculosis_ infections [23]. Accordingly, remarkable efforts have been devoted to establish convergent synthetic routes to access **5** that allow the preparation of analogues for SAR (structure-activity relationship) studies [24]. In this context, in 2009, [PERSON] and co-workers described a concise synthesis of capuramycin (**5**), starting from the partially protected uridine **2** (15 steps), in which the primary amide unit was conveniently generated by the hydration of the C\(\equiv\)N unit of intermediate **3** using [PtH{(PMe2O)2H}(PMe2 OH)] (**1**) (Scheme 3) [25]. The hydration reaction, performed in aqueous ethanol at 70 \({}^{\circ}\)C, with 5 mol% of **1**, allowed the quantitative conversion of **3** to the corresponding amide **4**. **Scheme 3. The Parkins catalyst in the synthesis of capuramycin. **  
**(-)-Huperzine A (**9**) is a tricyclic alkaloid produced by the Chinese herb** _Hupercia serrata_ [26], with intense contemporary interest in clinical application for treating neurodegenerative diseases [27, 28, 29]. Several total syntheses of **9** have been reported [27, 28, 29]. In one of the most recent and scalable (eight steps starting from (\(R\))-4-methyl-cyclohex-2-ene-1-one (**6**); 35%-45% overall yield), complex **1** was employed to promote the high-yield conversion of advanced nitrile intermediate **7** into amide **8** in aqueous ethanol (Scheme 4) [30]. From **8**, [PERSON]'s rearrangement of the amide group by means of [bis(trifluoroacetoxy)iodo]benzene (PIFA), followed by _in situ_ deprotection of the pyridone unit with iodotrimethylsilane (TMSI), delivered the desired alkaloid. **Scheme 4. ** The Parkins catalyst in the synthesis of (-)-huperzine A. The selective hydration of nitrile **10** to generate primary amide **11**, an advanced intermediate for the Nicolaou's synthesis of the marine natural product diazonamide A (**12**) [31,32], using [PtH{(PMeO)2H}(PMeOH)] (**1**) was described by [PERSON] and co-workers (Scheme 5) [33]. The reaction proceeded cleanly in aqueous ethanol at 120 \({}^{\circ}\)C with a catalyst loading of only 2 mol%, delivering **11** in 92% isolated yield. **Scheme 5. ** Synthesis of an amide intermediate for the preparation of diazonamide A. The welwittindolinones are a fascinating group of structurally unique metabolites isolated from blue-green algae that contain 3,4-bridged or spiro-cyclobutaneoxindole moieties [34,35]. Due to their challenging structures and their broad spectrum of biological activities, these compounds have attracted the attention of synthetic chemists for some time, although their complexity has prevented the completion of total syntheses for most of them thus far [36]. In an approach to welwittindolinone C isothi cyanate (welwistatin **17**), [PERSON] and co-workers have described the preparation of the related indole isocyanate derivative **16** starting from the vinylcyclohexanone **13** after 13 steps (Scheme 6) [37]. In this synthesis, the Parkins catalyst was employed to hydrate the encumbered nitrile **14**. A high loading of complex **1** (42 mol%) was, in this case, required to generate the bridgehead primary amide **15** in high yield (73%). In the presence of Pb(OAc)\({}_{4}\), amide **15** evolved into the final isocyanate **16** through the Baumgarten variant of the Hoffmann rearrangement. **Scheme 6. ** [PERSON]'s approach to the synthesis of welwistatin. In 2009, [PERSON] and [PERSON] developed a total synthesis of (\({}^{+}\))-geniposide (**21**), an iridoid \(\beta\)-glucoside of natural origin with anti-tumor and anti-inflammatory activity, starting from pivalate-protected lactol **18** (Scheme 7) [38].