Scheme 5a.
a Reagents and conditions: (i) ClCH2CH2Cl, DBU 1 equiv, rt, Ar, 3 h. (ii) NaI, Na2CO3, Bu4NBr, dioxane, Ar, reflux, 40 h. (iii) CH3I, dioxane, rt, 1 d. (iv) TFA/CH2Cl2/thioanisole, rt, 0.5 h.
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