Asymmetric Chlorination/Ring Expansion for the Synthesis of α-Quaternary Cycloalkanones
作者:Qin Yin、Shu-Li You
DOI:10.1021/ol5005565
日期:2014.3.21
A highly enantioselective chlorination/ringexpansion cascade for the construction of cycloalkanones with an all-carbon quaternary center was realized (up to 97% ee). Oxa-cyclobutanol substrates were employed for the first time in the ringexpansionreactions, affording the functionalized dihydrofuranones in excellent enantioselectivity.
the heavier halogens (bromine and iodine) second, the scope and limitations of the halogenative phase‐transfer methodology will be discussed and compared. An extension of the fluorination/semi‐pinacol reaction to the ring‐expansion of five‐membered allylic cyclopentanols will be also described, as well as some preliminary results on substrates prone to desymmetrization will be given. Finally, the present
The present manuscript describes a high-yielding enantioselective semipinacol transposition, initiated by an electrophilic iodination event. The title transformation makes use of the anionic phase-transfer catalysis (PTC) paradigm for chirality induction. Thus, when combined appropriately, the insoluble cationic iodinating reagent S9 and the lipophilic phosphoric acid L9 act as an efficient source
sulfonylation/semipinacol rearrangements of allylic alcohols were developed using cheap and stable RSO2Na (R = CF3, Ph) as reagents. Various β-trifluoromethyl and sulfonated ketones were obtained in moderate to excellent yields. This strategy provides a facile, direct, and complementary approach to construct all-carbon quaternary stereocenters. In addition, the reaction has the advantages of being chemical oxidant-free
Visible‐Light Photoredox‐Catalyzed Semipinacol‐Type Rearrangement: Trifluoromethylation/Ring Expansion by a Radical–Polar Mechanism
作者:Basudev Sahoo、Jun‐Long Li、Frank Glorius
DOI:10.1002/anie.201503210
日期:2015.9.21
semipinacol‐type rearrangement proceeding via 1,2 alkyl migration was developed. In this transformation, trifluoromethylation of the CC bond of α‐(1‐hydroxycycloalkyl)‐substituted styrene derivatives is followed by ringexpansion of the 1‐hydroxycycloalkyl group to deliver novel cycloalkanones with all‐carbon quaternary centers. The reaction proceeds via a radical–polar mechanism, with trifluoromethylation