Development of novel enantioselective catalytic reactions

The inverse electron demand Diels-Alder reaction between 2-pyrone-3-carboxylic acid and various vinyl ethers has been performed to attain the respective products with very high diastereoselectivity, which can be used for the synthesis of cycloheixenyl nucleosides (Scheme 1). [diagram]. Scheme 1. Highly diastereoselective Inverse Electron Demand Diels-Alder reaction Primary amino alcohols derived from natural amino acids have been found to be efficient organocatalysts for the cross-aldol reaction between acetone and activated ketones, affording the respective products with high enantioselectivity (Scheme 2). [diagram]. Scheme 2. The enantioselective cross-aldol reaction catalysed by leucinol A practical, highly stereoselective, two-step protocol for the alpha-allylation of aldehydes, starting from allyltrichlorosilanes, has been developed. As a result of the kinetic resolution in each step, virtually enantio- and geometrically pure linear homoallylic alcohols were obtained in high yield from the technical grade aliyltrichlorosilanes by using only 5 mol% of a chiral catalyst (Scheme 3). [diagram]. Scheme 3. The highly enantioselective alpha-allylation of aldehydes

In silico rationalisation of selectivity and reactivity in Pd-catalysed C-H activation reactions.

A computational approach has been developed to automatically generate and analyse the structures of the intermediates of palladium-catalysed carbon-hydrogen (C-H) activation reactions as well as to predict the final products. Implemented as a high-performance computing cluster tool, it has been shown to correctly choose the mechanism and rationalise regioselectivity of chosen examples from open literature reports. The developed methodology is capable of predicting reactivity of various substrates by differentiation between two major mechanisms - proton abstraction and electrophilic aromatic substitution. An attempt has been made to predict new C-H activation reactions. This methodology can also be used for the automated reaction planning, as well as a starting point for microkinetic modelling.EPSRC grant EP/K009494/1 (MK and SL) and the National Research Foundation, Prime Minister’s Office, Singapore under its CREATE programme, project “Cambridge Centre for Carbon Reduction in Chemical Technology” (LC and AL)

Catalytic asymmetric crotylation of aldehydes: application in total synthesis of (−)‐elisabethadione

A new, highly efficient Lewis base catalyst for a practical enantio- and diastereoselective crotylation of unsaturated aldehydes with E- and Z-crotyltrichlorosilanes has been developed. The method was employed as a key step in a novel asymmetric synthesis of bioactive serrulatane diterpene (À)-elisabethadione. Other strategic reactions for setting up the stereogenic centers included anionic oxy-Cope rearrangement and cationic cyclization. The synthetic route relies on simple, high yielding reactions and avoids use of protecting groups or chiral auxiliaries

Catalytic asymmetric crotylation of aldehydes: application in total synthesis of (−)‐elisabethadione

A new, highly efficient Lewis base catalyst for a practical enantio- and diastereoselective crotylation of unsaturated aldehydes with E- and Z-crotyltrichlorosilanes has been developed. The method was employed as a key step in a novel asymmetric synthesis of bioactive serrulatane diterpene (À)-elisabethadione. Other strategic reactions for setting up the stereogenic centers included anionic oxy-Cope rearrangement and cationic cyclization. The synthetic route relies on simple, high yielding reactions and avoids use of protecting groups or chiral auxiliaries

Asymmetric total synthesis of (-)-erogorgiaene and its C11 epimer and investigation of their antimycobacterial activity

A short, nine-step, highly enantioselective synthesis of (−)-erogorgiaene and its C-11 epimer is reported. The key stereochemistry controlling steps involve catalytic asymmetric crotylation, anionic oxy-Cope rearrangement and cationic cyclisation. (−)-Erogorgiaene exhibited promising antitubercular activity against multidrug-resistant strains of Mycobacterium tuberculosis

Highly stereoselective synthesis of z-homoallylic alcohols by kinetic resolution of racemic secondary allyl boronates

α to Z: Racemic α-chiral allyl boronates, which are readily synthesized from the respective primary allyl halides, undergo a highly efficient kinetic resolution in a face- and Z-selective allylation of aldehydes catalyzed by the chiral Brønsted acid (R)-TRIP (see scheme; Epin=tetraethylethylene glycol). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Organic & Biomolecular Chemistry Direct preparation of thiazoles, imidazoles, imidazopyridines and thiazolidines from alkenes †

A range of heterocycles, namely thiazoles, imidazoles, imidazopyridines, thiazolidines and dimethoxyindoles, have been synthesised directly from alkenes via a two-step ketoidoination/ cyclisation protocol. The alkene starting materials are themselves readily accessible using many different and well-established approaches, and allow access to a variety of heterocycles with excellent yields and regioselectivity

Research data supporting "Combination of enabling technologies to improve and describe the stereoselectivity of Wolff-Staudinger cascade reaction"

A new single-mode bench-top resonator was evaluated for the microwave-assisted flow generation of primary ketenes by thermal decomposition of alpha-diazoketones at high temperature. A number of amides and beta-lactams were obtained by in situ ketene generation and reaction with amines and imines respectively in good to excellent yields. The preferential formation of trans-configured beta-lactams was observed during the [2+2] Staudinger cycloaddition of a range of ketenes with different imines under controlled reaction conditions. Some insights into the mechanism of this reaction at high temperature are reported and a new web-based molecular viewer, which takes advantage from augmented reality (AR) technology, is also described for a faster interpretation of computed data.EPSRC [EP/K009494/1, EP/K039520/1 and EP/M004120/1

Cross-aldol reaction of isatin with acetone catalyzed by leucinol: a mechanistic investigation

Comprehensive mechanistic studies on the enantioselective aldol reaction between isatin (1a) and acetone, catalyzed by L-leucinol (3a), unraveled that isatin, apart from being a substrate, also plays an active catalytic role. Conversion of the intermediate oxazolidine 4 into the reactive syn-enamine 6, catalyzed by isatin, was identified as the rate-determining step by both the calculations (ΔG≠=26.1 kcalmol-1 for the analogous L-alaninol, 3b) and the kinetic isotope effect (kH/kD=2.7 observed for the reaction using [D6]acetone). The subsequent reaction of the syn-enamine 6 with isatin produces (S)-2a (calculated ΔG≠=11.6 kcalmol-1). The calculations suggest that the overall stereochemistry is controlled by two key events: 1) the isatin-catalyzed formation of the syn-enamine 6, which is thermodynamically favored over its anti-rotamer 7 by 2.3 kcalmol-1; and 2) the high preference of the syn-enamine 6 to produce (S)-2a on reaction with isatin (1a) rather than its enantiomer (ΔΔG≠=2.6 kcalmol-1)