A formal, highly stereoselective halo-Meyer-Schuster rearrangement of inactivated propargylic acetates to (Z)-α-haloenones has been reported, under metal free conditions. This cascade process involves a new class of intermediate, i.e., α,α-dihalo-β-acetoxyketones and mechanism to generate the α-haloenones, employing water as Lewis base. The outcome of the reaction is temperature-dependent, as room temperature, selectively provides α,α-dihalo-β-acetoxyketones whereas reactions at 100 °C give direct access to α-haloenones. Either type of product can be obtained in excellent yield. A suitable rationale for the observed high Z-selectivity for α-haloenones (based on conformational population) and distinct reaction rates for various N-halosuccinimide (NXS) reagents (based on C-X bond strengths) has also been provided. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Beeraiah Baire

Department Of Chemistry

Santu Sadhukhan

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Chemistry (Weinheim an der Bergstrasse, Germany)

Formal Halo-Meyer-Schuster Rearrangement of Propargylic Acetates through a Novel Intermediate and an Unexampled Mechanistic Pathway

An acid, HI promoted di-deiodination process for the synthesis of α-acetoxy/hydroxymethyl ketones from α′-acetoxy-α,α-dihaloketones has been reported. The process is very general in terms of structural diversity of both tertiary- as well as secondary-acetoxy possessing diiodoketones and found to be very efficient. The proposed mechanism involves as initial carbonyl activation by proton (acid) followed by the deiodination by Lewis base (iodide or water), for both the deiodination reactions. By extending this idea of acid activation during deiodination, further we have also developed a cascade conversion of propargylic acetates to corresponding α-acetoxy/hydroxymethyl ketones under metal free conditions. This strategy is unique and high yielding for total four functional group transformations, i. e., propargylic acetate to diiodoketone to mono-idodoketone to acetoxymethyl ketone to hydroxymethyl ketone. © 2019 Wiley-VCH Verlag GmbH &amp; Co. KGaA, Weinheim

ChemistrySelect

Metal Free Synthesis of α-Acetoxy/Hydroxymethyl Ketones from Propargylic acetates

The Meyer–Schuster rearrangement of propargylic alcohols is a transformation in organic synthesis known for almost a century. The products of this reaction—α,β-enones and their α-functionalized units—are highly important functional groups for various synthetic transformations. Two modifications of this classical reaction, which involves interception of the intermediate allenol (or its equivalent) by either electrophiles or nucleophiles, have attracted the attention of synthetic organic chemists. This Focus Review provides a detailed description of the development of these two strategies. © 2018 Wiley-VCH Verlag GmbH &amp; Co. KGaA, Weinheim

Asian Journal of Organic Chemistry

Intercepted Meyer–Schuster Rearrangements in Organic Synthesis

A mild, cascade methodology based on the modified Cadiot-Chodkiewicz reaction was developed for the stereoselective synthesis of trans-enynones. By this methodology, structurally divergent trans-enynones, which are embedded with sensitive functional groups, were synthesized. Control experiments suggested that the CuCl alone does not have a role in the isomerization step, whereas the CuCl-piperidine complex (formed during the cross coupling) may have a rate enhancing effect. Furthermore, additional sets of control experiments favor the involvement of unimolecular [1,2]-H shift rather than a homobimolecular proton abstraction during the isomerization step. © 2015 American Chemical Society.

Journal	Chemistry (Weinheim an der Bergstrasse, Germany)
Publisher	NLM (Medline)
ISSN	15213765
Open Access	No