Fraser-Reid coupling

In preliminary studies, Lu and Fraser-Reid had reported the efficient assembly of tetra-arabino derivative 178 by iterative couplings of donor 176 with NPG 177, also accessible by TBDPSOTf-catalyzed rearrangement of 176 (Scheme 5.39a) [104], They applied a similar protocol to the preparation of tetra-arabinan diol acceptor 182b (Scheme 5.39b). In this case, the protected ethanolamine 179 [84] was used as the first acceptor for the iterative sequence with NPOE donors 176 to obtain 180, and then with 181 to obtain 182a, which on treatment with thiourea furnished 3,5-diol 182b. 

K. L. Yu, S. Handa, R. Tsang, and B. Fraser-Reid, Carbohydrate-derived partners display remarkably high stereoselectivity in aldol coupling reactions, Tetrahedron 47 189 (1991). 

D. R. Mootoo, P. Konradsson, U. E. Udodong, and B. Fraser-Reid, Armed and disarmed n-pentenyl glycosides in saccharide couplings leading to oligosaccharides, J Am. Chem. Soc. 770 5583 (1988). 

Fraser-Reid s stereocontrolled synthesis of the Woodward reserpine precursor 195 relied upon a tandem 5-exol6-exo radical cyclization of pyranose-derived dienes [76-77]. As outlined in Scheme 36, a,P-unsaturated ester 188 was prepared by free radical coupling of iodide 187 with a tin acrylate. After hydrolysis of 188 (MeONa, MeOH, 100%) to give primary alcohol 189, the silicon tethered diene 190 was installed by silylation. Treatment of 190 with n-BujSnH led to the desired cage molecule 192 in high yield via a 5-exo-trig cyclization to intermediate 191 followed by a 6-exo cyclization. Tamao oxidation of tricycle 192 led to diol... 

Sunay, U. Fraser-Reid, B. Synthetic studies relating to the C1-C9 eastern" half of rosara-micin. Tetrahedron Lett. 1986, 27, 5335-5338. Smith, A. B. Pitram, S. M. Boldi, A. M. Gaunt, M. J. Sfouggatakis, C. Moser, W. H. Multicomponent linchpin couplings. Reaction of dithiane anions with terminal epoxides, epichlorohydrin, and vinyl epoxides efficient, rapid, and stereocontrolled assembly of advanced fragments for complex molecule synthesis./. Am. Chem. Soc. 2003, 125, 14435— 14445. 

Fraser-Reid B, Wu Z, Andrews CW, Skowronski E. Torsional effects in glycoside reactivity saccharide couplings mediated by acetal protecting groups. J. Am. Chem. Soc. 1991 113 1435-1437. 

Fraser-Reid and co-workers designed a photolabile o-nitrobenzylic linker 268, which was used in the synthesis of a branched trimannan oligosaccharide 271 (O Scheme 41) [139]. Differentially protected NPG 269 was coupled to the resin via linker 268. Selective removal of the C6 chloroacetyl and C3 acetyl groups, followed each by mannosylation (NIS/TESOTf) with NPG 64, afforded trimannan 271, in 42% overall yield after photolytic cleavage. 

The reaction has been most often applied to the synthesis of cycloalkenes, since the acyclic version shows low stereoselectivity. A modification of the original Tipson- ohen conditions has been developed by Fraser-Reid and coworkers for the elaboration of carbohydrate derivatives, in which sodium iodide in conjunction with Zn or Zn-Cu couple in refluxing DMF is used to effect the elimination. As can be seen from the examples shown in equations (14) and (15), the reaction proceeds with equal ease for both cis and trans isomers. 

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