8 research outputs found
Iridium-Catalyzed Allylic Fluorination of Trichloroacetimidates
A rapid allylic fluorination method utilizing trichloroacetimidates in conjunction with an iridium catalyst has been developed. The reaction is conducted at room temperature under ambient air and relies on Et<sub>3</sub>N¡3HF reagent to provide branched allylic fluorides with complete regioselectivity. This high-yielding reaction can be conducted on a multigram scale and shows considerable functional group tolerance. The use of [<sup>18</sup>F]KF¡Kryptofix allowed <sup>18</sup>F<sup>â</sup> incorporation in 10 min
Iridium-Catalyzed Allylic Fluorination of Trichloroacetimidates
A rapid allylic fluorination method utilizing trichloroacetimidates in conjunction with an iridium catalyst has been developed. The reaction is conducted at room temperature under ambient air and relies on Et<sub>3</sub>N¡3HF reagent to provide branched allylic fluorides with complete regioselectivity. This high-yielding reaction can be conducted on a multigram scale and shows considerable functional group tolerance. The use of [<sup>18</sup>F]KF¡Kryptofix allowed <sup>18</sup>F<sup>â</sup> incorporation in 10 min
Dynamic Kinetic Resolution of Allylic Azides via Asymmetric Dihydroxylation
The
catalytic enantioselective preparation of densely functionalized
amines is a fundamental synthetic challenge. To address this challenge,
we report for the first time that the Winstein rearrangement can be
enlisted as the racemization pathway in a dynamic kinetic resolution
of allylic azides. Alkene functionalization by Sharpless dihydroxylation
affords tertiary azides in excellent enantioselectivity (up to 99:1
er). This approach establishes the chirality of the tertiary azide,
obviates the need to directly forge either a congested CâN
or CâC bond at the new nitrogenous stereocenter, and establishes
additional functionality. Several examples demonstrate further elaboration
of this functionality
Regiocontrolled Wacker Oxidation of Cinnamyl Azides
A highly regioselective
Wacker oxidation has been developed for
the oxidation of cinnamyl azides. The catalytic oxidation tolerates
the azide functionality, and more than 15 β-azido ketones were
isolated (25â92% yield). High regioselectivity for the aryl
ketone is observed in all cases. A robustness screen was conducted
to determine functional group tolerance. The products of the oxidaiton
can be readily diversified
Stereoselective Dynamic Cyclization of Allylic Azides: Synthesis of Tetralins, Chromanes, and Tetrahydroquinolines
This
report describes the stereoselective synthesis of 3-azido-tetralins,
-chromanes, and -tetrahydroquinolines via a tandem allylic azide rearrangement/FriedelâCrafts
alkylation. Exposure of allylic azides with a pendant trichloroacetimidate
to catalytic quantities of AgSbF<sub>6</sub> proved optimal for this
transformation. This cascade successfully differentiates the equilibrating
azide isomers, providing products in excellent yield and selectivity
(>25 examples, up to 94% yield and >25:1 dr). In many cases,
the reactive
isomer is only a trace fraction of the equilibrium mixture, keenly
illustrating the dynamic nature of these systems. We demonstrate the
utility of this process via a synthesis of hasubanan
Copper-Catalyzed [<sup>18</sup>F]Fluorination of (Mesityl)(aryl)iodonium Salts
A practical, rapid, and highly regioselective
Cu-catalyzed radiofluorination
of (mesityl)Â(aryl)Âiodonium salts is described. This protocol utilizes
[<sup>18</sup>F]ÂKF to access <sup>18</sup>F-labeled electron-rich,
-neutral, and -deficient aryl fluorides under a single set of mild
conditions. This methodology is applied to the synthesis of protected
versions of two important radiotracers: 4-[<sup>18</sup>F]Âfluorophenylalanine
and 6-[<sup>18</sup>F]ÂfluoroDOPA
Evidence for a Sigmatropic and an Ionic Pathway in the Winstein Rearrangement
The
spontaneous rearrangement of allylic azides is thought to be
a sigmatropic reaction. Presented herein is a detailed investigation
into the rearrangement of several allylic azides. A combination of
experiments including equilibrium studies, kinetic analysis, density
functional theory calculations, and selective <sup>15</sup>N-isotopic
labeling are included. We conclude that the Winstein rearrangement
occurs by the assumed sigmatropic pathway under most conditions. However,
racemization was observed for some cyclic allylic azides. A kinetic
analysis of this process is provided, which supports a previously
undescribed ionic pathway
Evidence for a Sigmatropic and an Ionic Pathway in the Winstein Rearrangement
The
spontaneous rearrangement of allylic azides is thought to be
a sigmatropic reaction. Presented herein is a detailed investigation
into the rearrangement of several allylic azides. A combination of
experiments including equilibrium studies, kinetic analysis, density
functional theory calculations, and selective <sup>15</sup>N-isotopic
labeling are included. We conclude that the Winstein rearrangement
occurs by the assumed sigmatropic pathway under most conditions. However,
racemization was observed for some cyclic allylic azides. A kinetic
analysis of this process is provided, which supports a previously
undescribed ionic pathway