Abstract
Synthesis of carboxy-polyethylene glycol-amine (CA (PEG)(n)) via oxa-Michael addition of amino-polyethylene glycols to either acrylates or propiolates was investigated. Compared with the oxa-Michael addition to acrylates, the corresponding addition to propiolates was found to proceed under mild reaction conditions and afford the adducts in high yields from a broad scope of substrates. A two-step efficient and convenient synthesis of benzyl [1-C-14]-propiolate from (CO2)-C-14 was therefore developed and utilized as a common synthon to afford practical and high yielding access to [1-C-14]-CA (PEG)(n).