Asymmetric synthesis olefins

There have been several reviews of asymmetric synthesis via chiral organoboranes (6,8,378,382,467—472). Asymmetric induction in the hydroboration reaction may result from the chiraHty present in the olefin (asymmetric substrate), in the reagent (asymmetric hydroboration), or in the catalyst (catalytic asymmetric hydroboration). 

Ru(OCOCH2)2[(3)-BINAP]-(106)-catalyzed reduction of precursor olefin (107). The asymmetric synthesis of analgesic tetrahydroisoquinolines makes use... 

Following Uskokovic s seminal quinine synthesis [40], Jacobsen has very recently reported the first catalytic asymmetric synthesis of quinine and quinidine. The stereospecific construction of the bicyclic framework, introducing the relative and absolute stereochemistry at the Cg- and expositions, was achieved by way of the enantiomerically enriched trans epoxide 87, prepared from olefin 86 by SAD (AD-mix (3) and subsequent one-pot cyclization of the corresponding diol [2b], The key intramolecular SN2 reaction between the Ni- and the Cg-positions was accomplished by removal of the benzyl carbamate with Et2AlCl/thioanisole and subsequent thermal cyclization to give the desired quinudidine skeleton (Scheme 8.22) [41],... 

Oxidation of cyclic phosphonoformaldehyde dithioacetal, using the Modena protocol, yields the trans disulfoxide 121 in excellent enantiomeric excess. Then 121, via HWE olefination and oxidation of the double bond has been used for the diastereoselective preparation of spirocyclic his-sulfinyl oxiranes (new versatile intermediates in asymmetric synthesis) [79] (Scheme 37). 

Satoh T, see Miura M (2005) 14 1-20 Satoh T, see Miura M (2005) 14 55-84 Savoia D (2005) Progress in the Asymmetric Synthesis of 1,2-Diamines from Azomethine Compoimds. 15 1-58 Schmalz HG, Gotov B, Bottcher A (2004) Natmal Product Synthesis. 7 157-180 Schmidt B, Hermanns J (2004) Olefin Metathesis Directed to Organic Synthesis Principles and Applications. 13 223-267... 

The modification of chiral enamines enables the asymmetric nitro-olefination of oxyin-doles, as shown in Eq. 4.98.124 An enantioselective synthesis of (-)-psudophyrnaminol is accomplished using this reaction. 

The strategy based on asymmetric nitro-olefination is further applied to a total synthesis of (-)-horsfiline (Eq. 4.99).125... 

A hydrosilylation/cyclization process forming a vinylsilane product need not begin with a diyne, and other unsaturation has been examined in a similar reaction. Alkynyl olefins and dienes have been employed,97 and since unlike diynes, enyne substrates generally produce a chiral center, these substrates have recently proved amenable to asymmetric synthesis (Scheme 27). The BINAP-based catalyst employed in the diyne work did not function in enyne systems, but the close relative 6,6 -dimethylbiphenyl-2,2 -diyl-bis(diphenylphosphine) (BIPHEMP) afforded modest yields of enantio-enriched methylene cyclopentane products.104 Other reported catalysts for silylative cyclization include cationic palladium complexes.105 10511 A report has also appeared employing cobalt-rhodium nanoparticles for a similar reaction to produce racemic product.46... 

It is well documented that hydrosilylation of alkyl-substituted terminal olefins catalyzed by transition metal complexes proceeds with high regioselectivity in giving linear hydrosilylation products which do not possess a stereogenic carbon center.2 It follows that the asymmetric synthesis by use of the hydrosilylation of alkyl-substituted... 

The asymmetric oxidation of organic compounds, especially the epoxidation, dihydroxylation, aminohydroxylation, aziridination, and related reactions have been extensively studied and found widespread applications in the asymmetric synthesis of many important compounds. Like many other asymmetric reactions discussed in other chapters of this book, oxidation systems have been developed and extended steadily over the years in order to attain high stereoselectivity. This chapter on oxidation is organized into several key topics. The first section covers the formation of epoxides from allylic alcohols or their derivatives and the corresponding ring-opening reactions of the thus formed 2,3-epoxy alcohols. The second part deals with dihydroxylation reactions, which can provide diols from olefins. The third section delineates the recently discovered aminohydroxylation of olefins. The fourth topic involves the oxidation of unfunc-tionalized olefins. The chapter ends with a discussion of the oxidation of eno-lates and asymmetric aziridination reactions. 

Allylic alcohol derivatives are quite useful in organic synthesis, so the asymmetric synthesis of such compounds via asymmetric hydrogenation of dienyl (especially enynyl) esters is desirable. The olefin functionality preserves diverse synthetic potential by either direct or remote functionalization. Boaz33 reported that enynyl ester and dienyl ester were preferred substrates for asymmetric hydrogenation using Rh-(Me-DuPhos) catalyst [Rh(I)-(R,R)-14], and products with extremely high enantioselectivity (>97%) were obtained (Schemes 6-11 and 6-12). 

Optically active aldehydes are important precursors for biologically active compounds, and much effort has been applied to their asymmetric synthesis. Asymmetric hydroformylation has attracted much attention as a potential route to enantiomerically pure aldehyde because this method starts from inexpensive olefins and synthesis gas (CO/H2). Although rhodium-catalyzed hydrogenation has been one of the most important applications of homogeneous catalysis in industry, rhodium-mediated hydroformylation has also been extensively studied as a route to aldehydes. 

Synthetic applications of the asymmetric Birch reduction and reduction-alkylation are reported. Synthetically useful chiral Intermediates have been obtained from chiral 2-alkoxy-, 2-alkyl-, 2-aryl- and 2-trialkylsllyl-benzamides I and the pyrrolobenzodlazeplne-5,ll-diones II. The availability of a wide range of substituents on the precursor benzoic acid derivative, the uniformly high degree of dlastereoselection in the chiral enolate alkylation step, and the opportunity for further development of stereogenic centers by way of olefin addition reactions make this method unusually versatile for the asymmetric synthesis of natural products and related materials. 

Optically active epoxides are important building blocks in asymmetric synthesis of natural products and biologically active compounds. Therefore, enantio-selective epoxidation of olefins has been a subject of intensive research in the last years. The Sharpless [56] and Jacobsen [129] epoxidations are, to date, the most efficient metal-catalyzed asymmetric oxidation of olefins with broad synthetic scope. Oxidative enzymes have also been successfully utilized for the synthesis of optically active epoxides. Among the peroxidases, only CPO accepts a broad spectrum of olefinic substrates for enantioselective epoxidation (Eq. 6), as shown in Table 8. 

Peroxidases have been used very frequently during the last ten years as biocatalysts in asymmetric synthesis. The transformation of a broad spectrum of substrates by these enzymes leads to valuable compounds for the asymmetric synthesis of natural products and biologically active molecules. Peroxidases catalyze regioselective hydroxylation of phenols and halogenation of olefins. Furthermore, they catalyze the epoxidation of olefins and the sulfoxidation of alkyl aryl sulfides in high enantioselectivities, as well as the asymmetric reduction of racemic hydroperoxides. The less selective oxidative coupHng of various phenols and aromatic amines by peroxidases provides a convenient access to dimeric, oligomeric and polymeric products for industrial applications. 

Jacobsen EN (1993) Asymmetric catalytic epoxidation of unfunctionalized olefins. In Ojimal (ed) Catalytic asymmetric synthesis. VCH, Weinheim,p 159... 

Asymmetric Synthesis Using a Chiral Molybdenum Catalyst In olefin metathesis, a double bond is cleaved and a double bond is formed. Thus, a chiral carbon center is not constructed in the reaction. To realize the asymmetric induction by ring-closing metathesis, there are two procedures a kinetic resolution and desym-metrization of symmetric prochiral triene. Various molybdenum complexes are synthesized in order to explore the viabihty of these approaches (Figure 6.2). 

Asymmetric Olefin Metathesis Using Ruthenium Catalysts Ruthenium catalysts for asymmetric synthesis have also been developed (Figure 6.3). 

The asymmetric synthesis of (+)-Codeine 432 devised by White and colleagues included a Beckmann rearrangement to introduce the nitrogen atom in the carbocyclic structure (equation 182). Even though two isomeric lactams 430 and 431 were obtained as a result of the rearrangement, the preferential migration of the bridgehead carbon atom produced 430 as the predominant isomer. The synthesis of the non-natural enantiomer of Codeine was completed after oxidation, olefin formation and reduction. 

Bartlett PA (1984) Olefin cyclization processes that form carbon-heteroatom bonds. In Hassner A (ed) Asymmetric synthesis, vol 3. Academic, Orlando, FL, p 411... 

---