New strategy for synthesis

Ogoshi and coworkers have developed a new strategy for synthesis of a chiral porphyrin, in which an achiral porphyrin is modified to have C2 symmetry (an intrinsic chiral porphyrin) by introducing achiral substituents. In Figure 8 the Ct symmetric intrinsic chiral porphyrins are shown. A series of chiral porphyrins were prepared in... 

El-Zaria, M. E. and Nakamura, H. 2009. New strategy for synthesis of mercaptoundecahydrododecaborate derivatives via click chemistry Possible boron carriers and visualization in cells for neutron capture therapy. Inorg. Chem. 48 11896-902. 

Huang, J.-F. Luo, H. Dai, S. (2006). A New Strategy for Synthesis of Novel Classes of Room-Temperature Ionic Liquids Based on Complexation Reaction of Cations.. Electrodiem. Soc., 153,9-13. 

It is not surprising that multistep synthesis of challenging and complex target molecules is an engine for the discovery of new synthetic principles and novel methodology which may have very broad application. Just as each component of structural complexity can signal a strategy for synthesis, each obstacle to the realization of a chemical synthesis presents an opportunity for scientific discovery. 

The reaction processes shown in Scheme 8 not only accomplish the construction of an oxepane system but also furnish a valuable keto function. The realization that this function could, in an appropriate setting, be used to achieve the annulation of the second oxepane ring led to the development of a new strategy for the synthesis of cyclic ethers the reductive cyclization of hydroxy ketones (see Schemes 9 and 10).23 The development of this strategy was inspired by the elegant work of Olah 24 the scenario depicted in Scheme 9 captures its key features. It was anticipated that activation of the Lewis-basic keto function in 43 with a Lewis acid, perhaps trimethylsilyl triflate, would induce nucleophilic attack by the proximal hydroxyl group to give an intermediate of the type 44. 

The selectivity for two-alkyne annulation can be increased by involving an intramolecular tethering of the carbene complex to both alkynes. This was accomplished by the synthesis of aryl-diynecarbene complexes 115 and 116 from the triynylcarbene complexes 113 and 114, respectively, and Danishefsky s diene in a Diels-Alder reaction [70a]. The diene adds chemoselectively to the triple bond next to the electrophilic carbene carbon. The thermally induced two-alkyne annulation of the complexes 115 and 116 was performed in benzene and yielded the steroid ring systems 117 and 118 (Scheme 51). This tandem Diels-Alder/two-alkyne annulation, which could also be applied in a one-pot procedure, offers new strategies for steroid synthesis in the class O—>ABCD. 

Double asymmetric synthesis and a new strategy for stereochemical control in organic synthesis [95]... 

Recently, Denmark and coworkers have developed a new strategy for the construction of complex molecules using tandem [4+2]/[3+2]cycloaddition of nitroalkenes.149 In the review by Denmark, the definition of tandem reaction is described and tandem cascade cycloadditions, tandem consecutive cycloadditions, and tandem sequential cycloadditions are also defined. The use of nitroalkenes as heterodienes leads to the development of a general, high-yielding, and stereoselective method for the synthesis of cyclic nitronates (see Section 5.2). These dipoles undergo 1,3-dipolar cycloadditions. However, synthetic applications of this process are rare in contrast to the functionally equivalent cycloadditions of nitrile oxides. This is due to the lack of general methods for the preparation of nitronates and their instability. Thus, as illustrated in Scheme 8.29, the potential for a tandem process is formulated in the combination of [4+2] cycloaddition of a donor dienophile with [3+2]cycload-... 

S. Ballut, A. Makky, B. Loock, J.-P. Michel, P. Maillard, and V. Rosilio, New strategy for targeting of photosensitizers. Synthesis of glycodendrimeric phenylporphyrins, incorporation into a liposome membrane and interaction with a specific lectin, Chem. Commun. (2009) 224—226. 

In processes (400 + 402)—>(403) and (400 + 402)—>(404), the possibility of introducing of auxiliaries at the C-6 atom is advantageous for the development of new strategies for asymmetric synthesis with participation of six-membered 3-bromo-substituted six-membered cyclic nitronates. 

All of these facts substantially extend the possibilities of using AN in organic synthesis. There are prerequisites for the development of new strategies for the organic synthesis involving silylation of AN as the key step. Of course, these aims will be realized in future. 

H Yajima, N Fujii, S Funakoshi, T Watanabe, E Murayama, A Otaka. New strategy for the chemical synthesis of proteins. Tetrahedron, 44, 805-819, 1988. 

The tricyclic sesquiterpene longifolene has served as a vehicle for the illustration of new strategies for organic synthesis.25 Both enantiomers have been obtained from natural sources (-i-)-longifolene occurs in several Firms species and is commercially available while the rare (—)-longifolene has been found in certain liver mosses.2 We elected to prepare (—)-longifolene 49 from the cyclohexa-1,4-diene 45, obtained from the Birch reduction-alkylation of benzoxazepinone 9 in 96% yield with a diastereomeric excess of greater than 98% (Scheme 13).22... 

Matsuo, L Isomura, M. Walton, R. Ajisaka, K., A new strategy for the synthesis of the core trisaccharide of asparagine-hnked sugar chains. Tetrahedron Lett. 1996,37, 8795-8798. 

In this chapter, we discuss the important role played by some key natural products in malaria chemotherapy. We focus on naturally occurring secondary metabolites that had substantially affected the control and treatment of malaria. Advances in the total synthesis of these compounds and derivatives, and their implications in new strategies for the development of new generation of antimalarial drugs are also discussed. 

The Cinchona tree remains the only economically practical source of quinine. Although the development of synthetic quinine is considered a milestone in organic chemistry, it has never been produced industrially as a substitute for naturally occurring quinine. Nevertheless, the implications of the total synthesis of quinine in new strategies for the development of safer and more efficient antimalarial drugs, as we will show in the course of the next paragraphs, is priceless. But, let us discuss this total synthesis first. 

The Catalysis Concept of Iminium Activation In 2000, the MacMillan laboratory disclosed a new strategy for asymmetric synthesis based on the capacity of chiral amines to function as enantioselective catalysts for a range of transformations that traditionally use Lewis acids. This catalytic concept was founded on the mechanistic postulate that the reversible formation of iminium ions from a,p-unsaturated aldehydes and amines [Eq. (11.10)] might emulate the equilibrium dynamics and 7i-orbital electronics that are inherent to Lewis acid catalysis [i.e., lowest unoccupied molecular orbital (LUMO)-lowering activation] [Eq. (11.9)] ... 

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