Jae Uk Jeong

The use of tetramethylguanidinium azide in non-halogenated solvents avoids potential explosion hazards

Tetramethylguanidinium azide was used in the quantitative conversion of glycosyl halides 1 – 5 to the corresponding glycosyl azides 10 – 14. The stereoselective reactions occurred with complete inversion at the anomeric centers. The titled reagent was also employed in the selective synthesis of pseudoglycosyl azide 16 and two steroidal azides 17 and 18. All reactions were carried out in non-halogenated solvents to avoid potential explosion hazards.

Synthesis of the South hexacyclic sterold unit of cephalostatin 7

Abstract Transformation of alcohol 3 to S-12H, a hexacyclic steroid bearing the requisite functionality and spiroketal stereochemistry of the symchiral South portion of cephalostatin 7 (1) is described.

Spiroketal equilibration: Interconversion of 1,6-dioxaspiro[4.4]nonanes and 1,6-dioxaspiro[4.5]decanes. Implications for the synthesis of cephalostatin 7☆

Abstract Acid-catalyzed equilibration of spiroketals 55H ββ and 55H αβ involves a two stage process whereby the 1,6-dioxaspiro[4.4]nonanes can be equilibrated under mild conditions to a pair of 1,6-dioxaspiro[4.5]decanes with preservation of the adjacent C-20 methyl stereocenter. Under more forcing conditions, both centers can be equilibrated in a reaction involving vinyl ether intermediate 10H .