A Catalytic Approach

RuO2 + HCl + CH3CN + Steroid-NaOCI (Commercial Bleach) + H2O  

Additionally, the use of multiple solvents was minimized, with savings of up to 30-40% in the reaction and isolation. This process was found to be cost competitive with minimized waste. 

There are many methods to brominate aromatic as well as aliphatic moieties [35]. Several involve the use of dibromodimethyUiydantoin (DBDMH) [36] and azoi-sobutyronitrile (AIBN) as a radical initiator, a combination which mainly bromi-nates aliphatic groups. DBDMH is synthesized by bromination of hydantoin with two moles of molecular bromine and yields two moles of hydrogen bromide as a waste by-product. 

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We chose benzyli dene acetone (4.39, Scheme 4.11) as a model dienophile for our studies. The uncatalysed Diels-Alder reaction of this compound with cyclopentadiene is slow, justifying a catalytic approach. Reaction of 4.39 with paraformaldehyde and dimethyl amine under acidic conditions in an aqueous ethanol solution, following a literature procedure, produced the HCl salt of 4.42 (Scheme 4.11). The dienophile was liberated in situ by adding one equivalent of base. 

Enantioselective deprotonations of meso substrates such as ketones or epoxides are firmly entrenched as a method in asymmetric synthesis, although the bulk of this work involves stoichiometric amounts of the chiral reagent. Nevertheless, a handful of reports have appeared detailing a catalytic approach to enantioselective deprotonation. The issue that ultimately determines whether an asymmetric deprotonation may be rendered catalytic is a balance of the stoichiometric base s ability... 

Catalysis is thus an enabling factor for sustainable energy, but a new approach to catalysis is needed in order to address the major changes that we will face in the near future. For this reason, IDECAT (a European Network of Excellence on Catalysis) organized in 2006 two thematic (brainstorm-like) workshops dedicated to the identification of a roadmap and priorities for a catalytic approach for sustainable energy production and for the direct catalytic conversion of renewable feedstocks into energy. 

Nomura N, Taira A, Tomioka T, Okada M (2000) A catalytic approach for cationic living polymerization Sc(OTf)3-catalyzed ring-opening polymerization of lactones. Macromolecules 33 1497-1499... 

A catalytic approach to the synthesis of arylglycines was proposed by Evans and coworkers using enantioselective amination of iV-acy 1 oxazolidinones [54], Metallo-bis(sulfonamide) complexes derived from chiral diamines are potential chiral catalysts. The magnesium-bis(sulfonamide) complex 109 was generated by treating (S,S)-bis(sulfonamide) 108 with dimethylmagnesium in dichloromethane (Scheme 50). 

Ayala M, Roman R, Vazquez-Duhalt R (2007) A catalytic approach to estimate the redox potential of heme-peroxidases. Biochem Biophys Res Commun 357 804-808... 

Although a catalytic approach was discussed in the initial publication [2b], stoichiometric amounts of the metal were usually required to achieve acceptable yields. In most cases, the readily prepared and air-stable alkyne-CojfCOlf, complexes (1) were heated (60- 120 C) with the alkene (occasionally under CO atmosphere), but long reaction times (often several days) were needed and the yields were frequently unsatisfactory. 

The first example of a catalytic approach to the selenium promoted conversion was reported by Torii, who described an oxyselenenylation-deselenenylation process using catalytic amounts of diphenyl diselenide [115]. The electrophilic species was produced from the diselenide by electrochemical oxidation in the presence of the alkene 233 in methanol or in water. As indicated in Scheme 36, the addition product is electrochemically oxidized to afford the selenoxide which by elimination gives the allylic ether or alcohol 234 and the phenylselene-nic acid which continues the cycle by adding again to the alkene 233. 

Early attempts to synthesize the natural alkaloids ( )-Vindorosine (71JA3299) and ( )-Vindoline (75JA6880) used a catalytic approach. Condensation of 1-methyltryptamine 176 with l-chlorobut-l-en-3-one provided the enaminone 177. Attempts to cyclize 177 failed until it was acetylated and then treated with boron trifluoride to give the tetracyclic indoline 178 in 35% yield. Subsequent synthetic manipulation led to the formation of ( )-Vindorosine 179a, Scheme 47 (71JA3299). ( )-Vindoline 179b was synthesized similarly (75JA6880). 

Alkenes, Arenes, and Alkanes. The catalytic cis-dihydroxylation of alkenes with iron complexes and Oxone as terminal oxidant has been reported by Che and coworkers. A wide range of electron-rich, electron-poor, aliphatic, aromatic, terminal, and o , -unsaturated alkenes were tolerated under the optimized reaction conditions. For example, methyl cinnamate could be transformed into the diol 9 on a 30 mmol scale with traces of undesired products 10 and 11 being isolated as side products (eq 98). Oxone has also been employed in the diastere-oselective dihydroxylation of alkenes in a catalytic approach to the Prevost-Woodward reaction. Up to 77% yield was obtained in the dihydroxylation of styrene however, NaI04 was found to be a superior oxidant affording the diol in 87% yield (eq 99). 

Giordano M, ladonisi A (2014) Tin-mediated regioselective benzylation and allylation of polyols applicability of a catalytic approach under solvtmt-fiee conditions. J Org Chem 79 (l) 213-222... 

A recent example L. Emmanuvel, T.M. A. Shaikh, A. Sudalai, Nal04 / LiBr-mediated diastereoselective dihydroxylation of olefins a catalytic approach to the Prevost-Woodward reaction, Org. Lett. 7 (2005) 5071-5074. 

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