The shown p-iodotoluene undergoes Sonogashira coupling with trimethylsilylacetylene, fluoride deprotection, catecholborane addition and water work-up to give P. P is treated either with NaOH then I₂ to give Q, or Br₂ then NaOMe to give R. Select Q and R.
Coupling and desilylation furnish p-tolylacetylene. Syn hydroboration gives an alkenylborane with a defined geometry. Base/iodine converts its C–B position to C–I with the iododeboronation geometry, producing the Z vinyl iodide Q. Bromination followed by base-induced elimination gives the opposite alkene geometry in the vinyl bromide R. The pair with Z iodide and E bromide is A. Tracking the aryl group and halogen across each C=C distinguishes the otherwise similar drawings.
More Organic Synthesis: Synthesis, reactions, mechanisms and selectivity involving the following classes of compounds – alkenes, alkynes, arenes, alcohols, phenols, aldehydes, ketones, carboxylic acids, esters, nitriles, halides, nitro compounds, amines and amides. Uses of Mg, Li, Cu, B, Zn, P, S, Sn and Si based reagents in organic synthesis. Carbon-carbon bond formation through coupling reactions – Heck, Suzuki, Stille, Sonogashira, Negishi, Kumada, Hiyama, Tsuji-Trost reactions; olefin metathesis, McMurry coupling and Buchwald-Hartwig amination reactions. Baylis-Hillman, Henry, Ritter, Sakurai, Tebbe olefination, Pauson-Khand and Nazarov cyclization reactions. Concepts of multistep synthesis – retrosynthetic analysis, strategic disconnections, synthons and synthetic equivalents. Atom economy and green chemistry, Umpolung reactivity – formyl and acyl anion equivalents. Selectivity in organic synthesis – chemo-, regio- and stereoselectivity. Protection and deprotection of functional groups. Concepts of asymmetric synthesis – resolution (including enzymatic), desymmetrization and use of chiral auxiliaries, organocatalysis. Carbon-carbon and carbonheteroatom bond forming reactions through enolates (including boron enolates), enamines and silyl enol ethers. Stereoselective addition to C=O groups (Cram, Prelog and Felkin-Anh models). Asymmetric aldol reactions – Evans reaction and proline catalyzed reaction. questions
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