Scheme 3. Alkylation of 17a and 17b To Give Analogues 18a–18c and Conversion of Isocyanate 19 To Give Thioethers 20a/b.

Reagents and conditions: (a) 2-chloroacetyl chloride, Et₃N, CH₂Cl₂, rt, overnight, 99%; (b) chloromethanesulfonyl chloride, Et₃N, CH₂Cl₂, rt, overnight, 85%; (c) NaH, THF, rt, 1–2 d, 4–99%; (d) DPPA, Et₃N, toluene, reflux, overnight, 17–65%.