Stereocontrolled approach synthesis

More recently, a stereocontrolled approach to the synthesis of allocolchicinoids was disclosed by Wulff and co-workers using a diastereoselective benzannulation of chromium carbene complexes, Fig. (16) [104,105],... 

The molecular complexities of these architecturally novel alkaloids have prompted intense studies to elaborate new and efficient methods and strategies for the synthesis of these products. Hence, several stereocontrol approaches have been developed to successfully construct the azaspirocyclic core of pinnaic acids and halichlorine, providing access to the formal total synthesis and highly stereoselectivity of these molecules (Christie et al. 2004 Zhang et al. 2005 Andrade and Martin 2005 Clive et al. 2005 and references cited therein). In particular, Danishefsky s research group has reported the first total synthesis of halichlorine (Trauner et al. 1999), supporting the previous conclusions regarding the structure of this alkaloid (Kuramoto et al. 1996 Arimoto et al. 1998), and has... 

Nakahara Y, lijima H, Ogawa T (1994) Stereocontrolled approaches to 0-glycopeptide synthesis. In Kovac P (ed) Synthetic oligosaccharides. Indispensable probes for the life sciences. ACS Symposium Series 560. American Chemical Society, Washington, p 249... 

A convergent, stereocontrolled total synthesis of the microtubule-stabilizing macrolides, epothilones A and B was achieved in the iaboratory of S.J. Danishefsky. During their investigations, they examined several approaches to construct these natural products. One possible strategy to introduce the Cl 5-hydroxyl group in an enantioselective fashion was to use Keck s asymmetric allylation method. Under standard conditions, the reaction provided the desired homoallylic alcohol in good yield and excellent enantioselectivity. 

The C14-C20 segment [108] Stereocontrolled formation of the C15 and chiral centers was the major problem encountered in the synthesis of this segment. A route starting from benzoate 165 [111] was selected after several attempts (Scheme 21). Standard chemical operations led to allylic alcohol 166. Stereocontrolled approach from the re-re face of the double bond in 166 was insured by a diborane-oxidative treatment of the bulky bis-boronate ester 167. 1,2-Diol protection, phenoxythiocarbonylation-hydride reduction [112], and deprotection led to diol 169, representing the C14-C20 segment. 

Aoyagi Y, Jain RP, Williams RM (2001) Stereocontrolled Asymmetric Synthesis of o -Hydroxy-/ -amino Acids. A Stereodivergent Approach. J Am Chem Soc 123 3472... 

The older approaches to the penam skeleton from acyclic precursors were based on the azetidinone ring formation by [2+2] cydoaddition of ketens or enolates to imines and by cyclization of fS-amino add precursors. These methods have been reviewed by Jastrzebski and Van Koten [76] and by Marchand-Brynaert and Brule [77]. Sheehan and Henery-Logan [78] developed the first total synthesis of natural penicillin in 1957. Baldwin and coworkers [79] reported the first highly stereocontrolled total synthesis of natural penicillin. Most of the recent methods for the synthesis of nonnatural penams, however, employ 2-azetidinones with appropriate functionalities for fused ring cyclization. 

Liu X, Shimizu M, Hiyama T (2004) A Facile stereocontrolled approach to CF3-substituted triarylethenes synthesis of panomifene. Angew Chem Int Ed 43 879-882... 

There are two main HDA approaches to stereocontrolled THP synthesis. The first uses a chiral auxiliary to direct ir-facial selectivity and generally proceeds through an endo transition state to give 2,6-cis cycloadducts. The second approach uses coordination of a chiral Lewis acid to activate the carbonyl while directing the approach of the diene to one face of the carbonyl dienophile. Several catalysts have been developed for the asymmetric HDA reaction with Jacobsen s Cr(lll) complexes [111, 112] exhibiting good to excellent enantioselectivities with a variety of substrates [113]. 

Kozmin SA, Iwama T, Huang Y, Rawal VH. An efficient approach to Aspidosperma alkaloids via [4-1-2] cycloadditions of aminosiloxydienes stereocontrolled total synthesis of ( )-tabersonine. Gram-scale catalytic asymmetric syntheses of (-l-)-tabersonine and (-l-)-16-methoxytahersonine. Asymmetric syntheses of (-l-)-aspidospermidine and (-)-quebrachamine. J. Am. Chem. Soc. 2002 124(17) 4628-4641. 

Hanessian S, Claridge S, Johnstone S. The power of visual imagery in synthesis planning. Stereocontrolled approaches to CGP-60536B, a potent renin inhibitor J. Org. Chem. 2002 67 4261 274. 

Couladouros EA, Vidali VP. Novel stereocontrolled approach to syn- and awO -oxepene-cyclogeranyl trans-fused polycyclic systems asymmetric total synthesis of (—)-aplysistatin, (+)-palisadin A, (+)-palisadin B, (+)-12-hydroxy-palisadin B, and the AB ring system of adociasulfate-2 and toxicol A. Chem. Eur. J. 2004 10(15) 3822-3835. 

Mehta, G. and Murthy, A.N. (1987) A general stereocontrolled approach to the 5-8 fused ring system application to the total synthesis of marine natural product ( )-precapneUadiene. /. Org. Chem., 52, 2875-2881. 

Samajdar, S., Patra, D., and Ghosh, S., Stereocontrolled approach to highly substituted cyclopentanones. Application in a formal synthesis of A O -capnellene, Tetrahedron, 54, 1789,1998. 

The necessity for producing large amounts of synthetic prostaglandins and analogs provided the impetus for a number of improvements in the bicyclo[2.2.1]heptene approach. Especially important was the development of an enantioselective modification for the synthesis of chiral prostanoids without resolution (1975) and the invention of a chiral catalyst for the stereocontrolled conversion of 15-keto prostanoids to either 15(5)- or 15(7 )- alcohols. 

Backvall et al. (240) have described a method which permits the stereocontrol-led preparation of 3a- and 3/ -hydroxytropane derivatives at will. The approach is related to the Kibayashi synthesis (92,93). 

The opening of cyclopropylcarbinols to homoallylic bromides constituted the first use of cyclopropyl compounds for the stereocontrolled synthesis of natural products. The cyclopropyl conjunctive reagents enhance the richness of this notion. The stereocontrolled opening of vinylcyclopropanes by a homopentadienyl proton shift provides an approach to trisubstituted olefins and thereby a new strategy. The fungal prohormone methyl trisporate B (224) as summarized in Scheme 15 illustrates this conceptual development97). 

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