The natural product ()-N-methylwelwitindolinone C

Chapter 22, Problem 22.113

(choose chapter or problem)

The natural product ()-N-methylwelwitindolinone C isothiocyanate is isolated from a blue-green algae and has been identified as a promising compound to treat drug-resistant tumors. Compound X (R = protecting group) was utilized as a key synthetic intermediate in the synthesis of the natural product (J. Am. Chem. Soc. 2011, 133, 1579715799). Compound X can be prepared in a ring-forming reaction from compound Y under strongly basic conditions (excess NaNH2). N O H SCN Cl N O H H RO N O OR Br X Y N-methylwelwitindolinone C isothiocyanate Several steps O H (a) Propose a plausible mechanism for conversion of Y into X under basic conditions. (b) When Y is converted into X, a minor side product of the reaction is a constitutional isomer of X which lacks a ketone group. Propose a structure for this side product. (Hint: Recall that enolates are ambident nucleophiles.)