CHEM 350 S’18 Problem Sessions Week 10 Solutions

1.BOX PROBLEMS: Provide the missing reactant(s), reagent(s), or major product(s) for the following reactions. Indicate stereochemistry where relevant. “No reaction” (“NR”) is a possible answer. A reagent box may contain more than one step! Alkyne is pKa 25. Any base that can deprotonate an alkyne in good yield must have a conjugate acid with pKa above 25! Alex Iyer CHEM 350 S’18 Problem Sessions Week 10 Sunday Provide two synthetic routes to the product mix shown, beginning with two DIFFERENT alkyne anions. Equally substituted alkyneBr atoms add to either side with equal probability Neville and Alex are competing for the Nobel Prize in Chemistry. Whoever can successfully synthesize but-2-yne from propyne will win the prize. If Neville and Alex both perform the synthesis successfully, they will share the prize. Neville chooses to perform the final step of his synthesis using ethanol as a solvent. Alex performs this step using the solvent tetrahydrofuran (THF), the structure of which can be found in his synthesis below. Neville’s proposed synthesis: Alex’s proposed synthesis: Who wins the Nobel Prize: Neville, Alex, both, or neither? _Alex_ Explain. In Neville’s final step, the alkyne anion deprotonates ethanol (acid-base happens first!), and all molecules of the alkyne anion are lost. Alex’s final step works because THF does not have a proton with pKa below 25.