The difference in reactivity of (-)-mono and dimenthyl vs. diethyl alkylphosphonates in the α-lithiation reaction:: Carbanionic synthesis of unknown (-)-dimenthyl 1-iodoalkylphosphonates and their first use in the radical iodine atom transfer addition (I-ATRA) and cyclisation (I-ATRC) reactions

Unknown (-)-dimenthyl and ethyl (-)-menthyl 1-iodoethylphosphonates were synthesized via I-lithio derivatives in 85-87% yields. Starting (-)-dimenthyl alkylphosphonates (R = Me, Et, i-Pr) were obtained in the Michaelis-Becker reaction (75-81% yields) and/or in the methylation reaction of the corresponding 1-lithio-alkylphosphonates (78-92% yields). An interesting concentration and time correlations, never observed for diethyl alkylphosphonates, were found for the metalation of bulky (-)-menthyl alkylphosphonates with /IBuLi and general reaction conditions for the carbanion generation were elaborated. The first example of the I-ATRA reaction of (-)-dimenthyl 1-iodoethylphosphonate with 1-hexene (AIBN) gave four diastereomers (1.6:1:1:0.4), separated into two pairs. The 1-ATRC reaction was not effective due to a steric hindrance around the reactive center. The X-ray analysis of (-)-dimenthyl methylphosphonate confirmed a considerable steric hindrance in higher (-)-dimenthyl alkylphosphonate esters in comparison to their diethyl analogs. (c) 2006 Published by Elsevier B.V.