Synthesis of an aryl phosphonate via the anionic phospho-fries rearrangement : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Chemistry at Massey University, Palmerston North, New Zealand
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Date
2002
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Massey University
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Abstract
Zearalenone (1) is a mycotoxin, which reduces fertility in sheep and leads to substantial production losses in New Zealand. Catalytic antibodies are proposed as a potential approach to reducing the problem. This thesis describes progress toward the synthesis of the aromatic fragment of a transition-state analogue for the hydrolysis of the zearalenone lactone. The key step in the synthesis is an anionic phospho-Fries rearrangement; this relatively novel transformation is reviewed. α-Resorcylic acid (36) was converted to three different substrates, each with potential to undergo the O→C transfer of the dimethylphosphoryl moiety. Methyl 3-dimethylphosphato-5-[[(1,1- dimethylethyl)dimethylsilyl]oxy]benzoate (117) was prepared in three steps and 40% overall yield, but the tert-butyldimethylsilyl (TBDMS) protecting group was found to be unstable to phenolate anions. (2-Bromo-3,5-dibenzyloxyphenyl)-1,3-dioxolane (154) was prepared but further elaboration required hydrogenolytic cleavage of the benzyl ethers which was incompatible with the Ar-Br linkage. Finally, Ethyl 3- dimethylphosphate-5-(p-methoxybenzoxy)benzoate (167) was prepared in three steps and 25% overall yield. Treatment with LDA at -78 °C led to the formation of 166, rather than the desired regioisomer 165, as a result of lithium preferentially coordinating to the phosphoryl and OPMB groups.
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Mycotoxins, Zeranol