Sequential Cyclization−Elimination Route to Carbohydrate-Based Oxepines

Abstract

A five-step preparation of carbohydrate-based oxepines from hept-1-enitols is presented. The hept-1-enitols were subjected to silyl protection and hydroboration/oxidation to give the protected heptan-1-itols. Swern oxidation of the homologated alcohols followed by sequential acetal formation/cyclization provided methyl 2-deoxyseptanosides that underwent elimination reactions to give the carbohydrate-based oxepines. The new sequence is an alternative to the ring-closing metathesis for the synthesis of carbohydrate-based oxepines from protected pyranose sugars. The product oxepines can serve as glycosyl donors in the synthesis of novel septanose carbohydrates. In addition, C-methylenealdehydo arabinofuranoside 16 was formed from 2-deoxyseptanoside 10 as the only product during protic acid mediated elimination reactions. This novel ring contraction complements other reported preparations of C-methylenaldehydo furanosides and underscores the acid-mediated reactivity introduced by competing eliminations between the C-1/C-2 and C-2/C-3 bonds.

Conformational analysis of methyl 5-O-methyl septanosides: effect of glycosylation on conformer populations

“…The gg rotamer was also observed in our earlier analysis of a-septanoside 1 and also in the solid state of a related methyl a-2-deoxy-septanoside. 26 In all of these cases, the gg rotamer is likely to be stabilized by a hyperconjugative interaction between r(C6-H6)!r * (C7-O7). The interactions between the C6 hydroxymethyl group and solvent 27 also influence which rotamers for 3 and 4 are accessed.…”

An oxepinone route to carbohydrate based oxepines

“…Routes to carbohydrate based oxepines have employed ring closing metathesis (RCM), 8 cyclization-elimination, 9 and photocycloisomerization strategies. 6 For example, McDonald has utilized a photocycloisomerization reaction to convert diols such as 1 to oxepines 2 (Eq.…”

Expanding the Scope of Aminosugars: Synthesis of 2‐Amino Septanosyl Glycoconjugates Using Septanosyl Fluoride Donors

“…This was noteworthy because, in a previous study that used 2-deoxy septanosides as intermediates, mixtures of cyclic acetal and acyclic dimethyl acetal were obtained under the same reaction conditions (e.g., 7 converted to 8 and 9, Scheme 2). [14] Second, the 1,2-trans glycosides were the exclusive products formed from the cyclization reaction. We argued that the protecting groups on the C2 amine were playing an important steric role for the selective formation of the cyclic acetal of a specific anomeric configuration.…”