An efficient synthesis of the inimer gamma-(2-bromo-2-methylpropionate)-epsilon-caprolactone (BMPCL)

Abstract

The original synthesis of gamma-(2-bromo-2-methylpropionate)-epsilon-caprolactone (BMPCL), in use since 1999, has an overall yield of 17% and uses a Cr(VI) reagent for a key oxidation. Despite these liabilities, this synthetic procedure has been reported in all subsequent uses of BMPCL. This is due to BMPCL’s desirable capacity as an inimer – the tertiary alpha-bromo ester functionality allows initiation of controlled radical polymerization while the strained lactone moiety can act as a monomer in ring-opening polymerizations. These orthogonal capacities make BMPCL useful for the synthesis of complex polymer architectures such as combs. This paper reports a higher yielding, telescoped BMPCL synthesis that reduces the use of toxic reagents. Utilizing a mild and near-quantitative activated-DMSO mechanism, the Swern oxidation, in place of pyridinium chlorochromate increases the yield by approximately half to 25% (average of three trials) while eliminating heavy metal usage. In an additional effort for synthetic efficiency, the number of chromatographic purifications was reduced from three to one.

Keywords

• Ring-opening polymerization
• controlled radical polymerization
• monomer synthesis
• initiator synthesis
• inimer synthesis