Sugar ring elaboration

Dondoni has elaborated this methodology to include C-glycosylated dihydro-pyrimidines/ The sugar residue can be a subunit in the aldehyde, 1,3-dicarbonyl, or urea consequently, substitution of the DHPM ring may occur in one of three places depending on which component originally contains the glycosidic residue. In the example... 

Curiously, the N-benzyl moiety on a variety of /3-lactams was untouched by the microwave-assisted CTH reactions. The authors further elaborated this interesting strategy for the reduction of the double bond in an unsaturated sugar moiety, without inducing the ring fission of the attached /1-lactam side chains (Scheme 46). 

In the event, Mitsunobu-type displacement of the unprotected hydroxyl of 24 delivered the iodinated sugar 25, which was then elaborated into acyclic iodohexenitol 26 via ring opening using activated zinc in refluxing ethanol, followed by reduction, tosylation and iodination. The pivotal radical cyclization/oxygenation of 26 was finally carried out in the presence of a catalytic amount of cobalt(salen) complex in air. This... 

Similar reactions were described by Vogel, using a naked sugar as a radical acceptor. The resulting product has to be further elaborated before it becomes a true C-linked disaccharide, with the key-step being a Baeyer-Villiger ring expansion [ 104,105] (O Scheme 48). 

Macrocyclic ring compounds (sec. 6.6.B) possess functionality and stereochemistry that can be as difficult to control as in acyclic systems. The use of cyclic precursors is of value here also. In the Corey synthesis of (-j-A-methylmaytansine, a sugar derivative, tri-O-acetyl-D-glucal (155), was used as a precursor to 156. This precursor contained the correct stereochemistry and functionality for elaboration of the eastern... 

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