Mechanistic Studies on the Base-Promoted Ring Opening of Glycal-Derived -Dibromocyclopropanes.

In the presence of a nucleophilic base, ring-fused -dibromocyclopropanes derived from d-glycals undergo ring opening to give 2-deoxy-2-(-bromomethylene)glycosides. Such cleavage of an exocyclic cyclopropane bond contrasts with the more usual silver-promoted ring-expansion reactions in which endocyclic bond cleavage occurs. Experimental and theoretical studies are reported which provide insights into the reaction mechanism and the origin of its kinetic selectivity for -configured bromoalkene products.

Total Synthesis and Bioactivity Studies of Fungal Metabolite (-)-TAN-2483B.

The first total synthesis of (-)-TAN-2483B, a fungal metabolite possessing a densely functionalized furo[3,4-]pyran-5-one framework, is achieved in 14 steps from d-mannose. Generation of the 2,6-pyran is by cyclopropane ring expansion followed by α-selective alkynylation. Julia-Kocienski olefination introduces the -propenyl side chain.

Norborn-2-en-7-ones as physiologically-triggered carbon monoxide-releasing prodrugs.

A prodrug strategy for the release of the gasotransmitter CO at physiological pH, based upon 3-bromo-norborn-2-en-7-one Diels-Alder cycloadducts of 2-bromomaleimides and 2,5-dimethyl-3,4-diphenylcyclopentadienone has been developed. Examples possessing protonated amine and diamine groups showed good water solubility and thermal stability. Half-lives for CO-release in TRIS-sucrose buffer at pH 7.

Synthesis of the (-)-TAN-2483B ring system via a D-mannose-derived cyclopropane.

The ring system of the fungal metabolite (-)-TAN-2483B has been synthesised, for the first time, from d-mannose, utilising a cyclopropanation/ring expansion sequence.

Synthesis of C-furanosides from a D-glucal-derived cyclopropane through a ring-expansion/ring-contraction sequence.

gem-Dibromocyclopropane 1, prepared from tri-O-benzyl-D-glucal, undergoes thermal and silver-promoted ring expansion in the presence of alcohols to give substituted oxepines. With further heating, ring contraction to highly substituted tetrahydrofurans follows. These represent C-furanosides, potentially useful as precursors to C-nucleosides and other carbohydrate mimics.

Synthesis of oxepines and 2-branched pyranosides from a d-glucal-derived gem-dibromo-1,2-cyclopropanated sugar.

The conversion of cyclopropane-fused carbohydrates into oxepines is an attractive method for accessing diverse members of the septanoside family of carbohydrate mimetics. 2-Bromooxepines are obtained through silver(I)-promoted thermal ring expansion of a d-glucal-derived gem-dihalocyclopropanated sugar. In contrast, cyclopropane ring cleavage under basic conditions leads to 2-C-branched pyranosides, not the 2-bromooxepine structures assigned in an earlier report.