3.16 The Semipinacol Rearrangements

Absence of Intermediates in the BINOL-Derived Mg(II)/Phosphate-Catalyzed Desymmetrizative Ring Expansion of 1-Vinylcyclobutanols

“…Of particular interest are the reactions in which the electron-deficient carbon (not necessarily a carbocation) is vicinal to an oxygen-containing carbon (the case of allylic alcohols). 5 In this case, the 1,2 migration of a carbon–carbon bond generates a carbonyl group consisting of a semipinacol rearrangement. 6 When the electron-deficient carbon generated during the halogenation step becomes tertiary, thus better supporting the positive charge, the resulting product is a carbonyl compound with a quaternary center in the α position ( Scheme 1 ; R 2 and R 3 ≠ H).…”

HNTf2-Catalyzed Synthesis of Hydrodibenzofurans by an Epoxidation/Semipinacol Rearrangement Cascade

“…Upon acid activation, the epoxide is expected to undergo ring-opening to form an ortho -quinone methide intermediate. Its propensity to rearomatize combined with the presence of a tertiary alcohol in close proximity would trigger a semipinacol rearrangement. , The resulting cyclohexanone unit could further form a cyclic hemiketal 2 with the phenolic hydroxy group . Moreover, we expect that the epoxidation could be compatible with the subsequent semipinacol rearrangement, thus representing a highly efficient one-pot cascade for the synthesis of hydrodibenzofurans with consecutive quaternary stereocenters.…”

Asymmetric Total Synthesis and Determination of the Absolute Configuration of (+)-Srilankenyne via Sequence-Sensitive Halogenations Guided by Conformational Analysis

“…A plausible mechanism for the formation of the major product 20b is shown in Scheme , in which the most stable conformer D of THP 19 would undergo the following sequence of events: (1) semipinacol rearrangement ( D → E ), (2) attack by a THF solvent molecule ( E → F ), and (3) opening of the resulting oxonium species by bromide ( F → 20b )…”