Two-directional approach

Encouraged by the success of the solution-phase approaches, we introduced a two-directional approach for oligosaccharide assembly on solid support. Two... 

Finally, Nakata recently reported the application of a radical-radical sequence in a two-directional approach to the B-E ring domain of maitotoxin.8 Treatment of dialdehyde 8 with Sml2 and MeOH gave lactone 9 and hydroxy ester 10 in excellent overall yield (Scheme 6.4).8... 

Zhu, T, Boons, G J, A two-directional approach for the solid-phase synthesis of trisaccharide libraries, Angew. Chem. Int. Ed., 37, 1898-1900, 1998. 

The preparation of species such as a-hydroxyphosphonates has been alluded to only briefly here (see Section 3.5). We would note two direct approaches that are available for the preparation of these materials, both involving nucleophilic addition to carbonyl carbon. One of these is referred to as the Abramov reaction that involves the addition of a fully esterified trivalent phosphorus acid to a carbonyl carbon followed by a dealkylation of the phosphorus ester site. This preparation is quite inefficient when ordinary ester linkages are used, but the use of silyl esters overcomes most of these difficulties and allows facile isolation of the target compounds (equation 30). Note that reaction occurs preferentially at the carbonyl carbon and not by displacement of halogen at carbon. Addition occurs preferentially at carbonyl carbon compared to displacement at a carbon-halogen linkage, and provides product if removal of the ester linkage is facile. 

Roe SJ, Stockman RA (2008) A two-directional approach to the anatoxin alkaloids second synthesis of homoanatoxin and efficient synthesis of anatoxin-a. Chem Commun (Camb) 3432-3434. doi 10.1039/b804304c... 

Dilger, A.K., Gopalsamuthiram, V., and Burke, S.D. (2007) A two-directional approach to a (-)-dictyostatin C11-C23 segment development of a highly diastereoselective, Idnetically-controlled Meerwein-Pondorf-Verley reduction. J. Am. Chem. Soc., 129, 16273-16277. 

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