Zinc inserts into the allylic C–Br bond, producing an organozinc reagent. Addition to benzaldehyde forms the new carbon–carbon bond and a zinc alkoxide. Intramolecular attack of that alkoxide on the ester closes a five-membered lactone with loss of ethoxide. The original exocyclic methylene remains on the α carbon of the lactone. This is the α-methylene-γ-lactone drawn in C.
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
GATE 2020 CY Q36– Find the major product of the shown bicyclic cyclopropyl ketone sequence: (i) KOH/EtOH;…
GATE 2020 CY Q37– The shown cyclopentadienylacetate reacts with (i) one equivalent 9-BBN, (ii) H₂O₂/NaOH to…
GATE 2020 CY Q43– The shown p-iodotoluene undergoes Sonogashira coupling with trimethylsilylacetylene,…
GATE 2019 CY Q21– The illustrated β-lactone reacts with Et₂AlCl in benzene at 5°C. Which major product is…
GATE 2019 CY Q22– Which model predicts the stereochemistry of EtLi addition to the illustrated α-methoxy…
GATE 2019 CY Q46– Two equivalents of ethyl acetoacetate react with formaldehyde using NaOEt in ethanol on…
