Stereoselective Synthesis of 1,3-Disaccharides through Diels-Alder Reactions: Part 2^[1

^[1]Dedicated to the memory of Prof. Giuseppe Capozzi (1941–2008), Dipartimento di Chimica Organica, Universita' di Firenze, who introduced and developed the use of oxothiones in hetero Diels-Alder reactions.

^]: Convenient Protecting Groups for Heterodienes and Conformational Evaluations

Abstract

Improved synthesis of 1,3-disaccharides, obtained diastereomerically pure by [4+2] hetero cycloadditions between glycals and α -thiono-β -keto-δ -lactones, has been reported. The choice of appropriate protecting groups for β -keto-δ -lactones, stable under cycloaddition conditions employed, sensibly shortened the synthesis of heterodienic precursors. The first example of a β -oxy-imino-δ -lactone synthesized from β -keto-δ -lactones was also reported. Molecular modeling and conformational evaluations about the cycloaddition features allowed tentatively rationalizing the experimental results.

Keywords:

• Disaccharides
• Diels-alder
• Stereoselective synthesis
• Conformational studies

ACKNOWLEDGEMENT

The authors thank Mrs. Brunella Innocenti for technical support. This work was financially supported by the University of Florence and MIUR (Rome) within the project PRIN 2006.

Notes

^a Calculated at 293°K.

^b HOMO of dienophile (3,4,6-tri-O-benzyl-D-glucal) = –9.37 eV.

^{[ 1 ]}Dedicated to the memory of Prof. Giuseppe Capozzi (1941–2008), Dipartimento di Chimica Organica, Universita' di Firenze, who introduced and developed the use of oxothiones in hetero Diels-Alder reactions.