The shown cyclopentadienylacetate reacts with (i) one equivalent 9-BBN, (ii) H₂O₂/NaOH to give P; then (i) MsCl/Et₃N, (ii) NaOH, (iii) H₂/(Ph₃P)₃RhCl to give Q. Select P and Q.
Bulky 9-BBN hydroborates the accessible alkene face, and oxidation replaces C–B by C–OH with retention, giving the allylic alcohol P drawn in A/B. Mesylation activates that alcohol without breaking its C–O bond. Hydrolysis generates the carboxylate, whose intramolecular displacement at the mesylate-bearing carbon closes the lactone with inversion. Rh-catalyzed hydrogenation removes the remaining C=C bond. The cis-fused lactone obtained after this inversion is Q in B.
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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