Synthesis of the DE Fragment

n-Bu4NI, 25 110 °C 2. TBSOTf, 2,6-lutidine, CH2CI2, 0- 25 °C (84% overall) 

With 143 in hand, the next set of operations sought to deoxygenate the C-6 position of ring D. In line with methods utilized for the same purpose in the synthesis of the E-ring precursor, its benzyli-dene group was initially cleaved through hydrogenation in EtOAc 

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Nicolaou KC, Mitchell HJ, Rodriguez RM, Fyllaktakidou KC, Suzuki H (1999) Total Synthesis of Eveminomicin 13,384-1 - Part 3 Synthesis of the DE Fragment and Completion of the Total Synthesis. Angew Chem Int Ed 38 3345... 

The iodoetherification strategy was applied to the synthesis of the smaller fragment coupling component 109 as well (Scheme 16). Silylation of alcohol 104 [30] (76% de) allowed the separation of the pure desired diastereomer, which in turn was subjected to hydroboration/oxidation, sulfide formation with thiol 105, and oxidation to give sulfone 106. The requisite y-triethylsilyloxy alkene functionality in 107 was constructed as a diastereomeric E) Z)=l.2 l mixture by another sulfone-based olefination of aldehyde 90 with 106. Treatment of 106 with... 

The total synthesis of the naturally occurring guaiane (+)-alismol was accomplished by G.L. Lange and co-workers using a free radicai fragmentation/eiimination sequence of an initial [2+2] de Mayo photocycloadduct. ... 

Approaches to dimethyl diacetoxymedicagenate (126) have resulted in the synthesis of the ab and de fragments (127) and (128). The compound (129) has been devised as a useful intermediate in a route to -amyrin. Stereoselective... 

In the synthesis of the C1-C12 fragment of amphidinolide Tl, syn aldol adduct 77 was prepared in 92% yield as a single diastereomer by the Crimmins modified Evan s strategy (TiCU with (-)-sparteine). This protocol was also used to install the stereocenters at the C4 and C5 in 80 with excellent diastereoselectivity (96% de) in the total synthesis of (-)-bitungolide F. In the total synthesis of cruentaren B, the Crimmins modified condition was used in the Evans syn aldol reaction, giving adduct 82 in excellent yield and diastereoselectivity (92%, 98% de). ... 

De Brabander, J., Kulkami, B.A., Garcia-Lopez, R., and Vandewalle, M. (1997) Bryostatin a novel asymmetric synthesis of the C27-C34 fragment starting from (R)-carvone as chiral template. Tetrahedron Asymmetry, 8,1721-1724. 

Most of the synthetic reactions leading to substituted carbon compounds can be re> versed. Reiro-a do or /le/fo-Diels-Alder reactions, for example, are frequently used in the de-gradative fragmentation of complex molecules to give simpler fragments. In synthesis, such... 

Lopez-Rodriguez, M.L., Ayala, D., Viso, A., Benhamu, B., Fernandez de la Pradilla, R., Zarza, F. and Ramos, J.A. (2004) Synthesis and structure-activity relationships of a new model of arylpiperazines. 7. Study of the influence oflipophilic factors at the terminal amide fragment on 5-HT1A affinity/selectivity. Bioorganic and Medicinal Chemistry, 12, 1551-1557. 

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