Reductive Studies on 3-Oxidopyrylium-alkene [5 + 2] Cycloadducts: Access to Some Hydroxy Cycloheptenoids

Abstract

The scope of nickel boride as a versatile reducing reagent is extended to the 3-oxidopyrylium-alkene [5 + 2] cycloadducts. In this report, we demonstrate that nickel boride is capable of one-pot 1,2- and 1,4-reduction of enones present in the cycloadducts in good yields. Subsequent elaboration of the cycloadducts towards synthesis of functionalized cycloheptenoid derivatives devoid of the oxa-bridge is also explored.

Keywords:

• [5 + 2] Cycloaddition
• cycloheptenoids
• nickel boride
• oxa-bridge
• 3-oxidopyrylium

ACKNOWLEDGMENT

Financial support from the University Grants Commission, New Delhi, India, is gratefully acknowledged.

Notes

^a It is already established that the reducing species is nickel boride, generated in situ, and not sodium borohydride. See Ref. 4.

^b Yields reported are after purification by column chromatography.

^c All reactions are carried out on a 1-mmol scale.

^a Yields reported are after purification by column chromatography.

^b All reactions are carried out on a 1-mmol scale.

^a All compounds are characterized by spectroscopic data.

^b Yields reported are after purification by column chromatography.