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 |
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Authors: | Piotr Ba?czewski Aldona Szadowiak Tomasz Bia?as Ma?gorzata Szyrej |
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Affiliation: | a Department of Heteroorganic Chemistry, Center of Molecular and Macromolecular Studies, Polish Academy of Sciences, 90-363 ?ód?, Sienkiewicza 112, Poland b Institute of Chemistry and Environmental Protection, Jan D?ugosz University, 42-200 Cze¸stochowa, Armii Krajowej 13/15, Poland |
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Abstract: | Unknown (−)-dimenthyl and ethyl (−)-menthyl 1-iodoethylphosphonates were synthesized via 1-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 n-BuLi 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 I-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. |
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Keywords: | Metalation Ethyl (&minus )-menthyl phosphonate (&minus )-Dimenthyl phosphonate Steric hindrance Asymmetric amplification Radical reaction |
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