Stereoselective synthesis of conjugated fluoro enynes
1Department of Chemistry, The City College and The City University of New York, 160 Convent Avenue, New York, New York 10031, United States.
Abstract:
Metalation-electrophilic fluorination of TMS- and TIPS-protected 1,3-benzothiazol-2-yl (BT) propargyl sulfones gave corresponding BT fluoropropargyl sulfones, Julia-Kocienski reagents for the synthesis of fluoro enynes. Both reagents reacted with aldehydes under mild DBU- or LHMDS-mediated conditions, giving high yields of conjugated fluoro enynes with E-stereoselectivity. In comparison to DBU-mediated reactions, stereoselectivity was higher in low-temperature LHMDS-mediated reactions. Two ketones were shown to react as well, using LHMDS as base. In situ removal of the TMS group gave terminal conjugated 2-fluoro 1,3-enynes. Synthetic utility of the fluoro enynes was demonstrated by conversion to internal alkynes and to stereoisomeric fluoro dienes via Sonogashira and Heck couplings.
Related Concept Videos
[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
Thermal Electrocyclic Reactions: Stereochemistry
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Synthesis of α-Substituted Carbonyl Compounds: The Stork Enamine Reaction
Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry
Diels–Alder Reaction Forming Cyclic Products: Stereochemistry
Regioselective Formation of Enolates


