Fluorous Boc (FBoc) Carbamates: New Amine Protecting Groups for Use in Fluorous Synthesis

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Abstract
The first fluorous variants of the Boc (tert-butyloxycarbonyl) group have been prepared and tested for their suitability as nitrogen protecting groups. A group with two fluorous chains and an ethylene spacer, (RfCH2CH2)2(CH3)COC(O)−, was readily attached to a representative amine but was difficult to cleave. In contrast, groups with two fluorous chains and a propylene spacer, (RfCH2CH2CH2)2(CH3)COC(O)−, or one fluorous chain and an ethylene spacer, (RfCH2CH2)(CH3)2COC(O)−, were readily formed and cleaved. The fluorous alcohol component of the FBoc group can be removed by evaporation and can be recovered and reused. The utility of the new FBoc group (C8F17CH2CH2)(CH3)2COC(O)− was demonstrated in 16 and 96 compound library synthesis exercises. Separations can be achieved either by manual, parallel fluorous solid-phase extraction, or automated, serial fluorous chromatography. The results provide additional confirmation of the value of “light” fluorous synthesis techniques, and the new fluorous Boc groups expand the applicability of fluorous synthesis techniques to many classes of nitrogen-containing organic compounds.