Rearrangements of Cyclic Sugars

SCHEME 8.29 Synthesis of carba-pyranoses using Sml2 induced pinacol coupling. 

SCHEME 8.31 Synthesis of carba-pyranoses from the product of the Ferrier-II rearrangement. 

SCHEME 8.33 Synthesis of carba-glucasamine using the Ferrier-II rearrangement. 

SCHEME 8.34 Synthesis of a carba-pyranoside using a Ti(IV) induced rearrangement. 

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One of the most common methods of the formation of the carbocyclic ring from the normal sugar ring is undoubtedly the Ferrier-H rearrangement discovered by Ferrier in 1979 [10]. It is based on an HgCl2-catalyzed rearrangement of unsaturated sugars with the C5-C6 (for pyranosides) or C4-C5 (for furanosides) exo-cyclic double bond. This method is discussed in many excellent reviews [11-13]. Such unsaturated... 

Aldehydes can be converted into amides by a Schmidt rearrangement (see Schmidt reaction, under Section 9.3.2.2). This reaction is particularly interesting for the formation of sugar lactams [187]. When aldehydes are treated with a-azido alcohols in the presence of acid, the rearrangement yields cyclic imidates [188]. Nitriles can be obtained directly in high yields by reacting aldehydes with triazidochlorosilane [189]. 

The first example of a methoxy-group participation in sugars was reported by Lemieux and Fraser-Reid 7) who observed 1,3,4,6-tetra-O-acetyl-2-0-methyl-D-glucop3U-anose (4) as one of the products of bro-minolysis of methyl 3,4,6-tii-0-acetyl-2-deoxy-2-iodo- -D-mannopyra-noside ffj in the presence of silver acetate. The cyclic methoxonium ion (2) was indicated to be an intermediate in this rearrangement, giving rise to the product either by direct nucleophilic attack of acetate ion or... 

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