In 2005, the ACS Green Chemistry Institute (GCI) and the global pharmaceutical corporations developed the ACS GCI Pharmaceutical Roundtable to encourage the development of green chemistry and green engineering in the pharmaceutical industry. The Roundtable has established a list of key research areas including the direct nucleophilic reactions of alcohols. The substitution of activated alcohols is a frequently used approach for the preparation of active pharmaceutical ingredients. Alcohols are transformed into the reactive halides or sulfonate esters, thereby allowing their reaction with nucleophiles. Although the direct nucleophilic substitution of an alcohol should be an attractive process, as one of the byproducts from the reaction yields water, hydroxide is a poor leaving group that hinders the reaction. Recently, the direct substitution of allylic, benzylic, and tertiary alcohols has been achieved through an SN1 reaction with catalytic amounts of Brønsted or Lewis acids. In this review, the approaches leading to a greener process are examined in detail, and the advances achieved to date in this important transformation are presented.

The development of novel and efficient catalytic methodologies for the stereoselective preparation of chiral aziridines is an important synthetic target.[1] Aziridines constitute a key structural feature of several classes of natural products and are extremely versatile building blocks that can undergo synthetically useful transformations.[2] The catalytic asymmetric aziridinations of olefins provide direct and useful access to such a valuable scaffold, and great efforts and progress have been made in this field.[3] However, to our knowledge, a general and highly stereoselective aziridination of simple a,b-unsaturated enones is still lacking. [4,5] Herein, we report an organocatalytic solution to this synthetic problem that is founded upon the use of a readily available chiral primary amine catalyst salt as well as on a rationally designed N-centered nucleophile.Previously reported asymmetric aziridinations of enones have severe restrictions in scope, as only chalcones are suitable substrates: metal-based systems [4] can provide highly enantioenriched compounds protected as N-tosyl derivatives, a protecting group that can prove to be difficult to remove, whereas two ingenious organocatalytic entries to nonprotected aziridines, showing moderate enantioselectivity (up to 67 % ee), were recently reported through the use of chiral tertiary amines. [5] Recently, the spectacular advances achieved in the field of chiral secondary amine catalysis [6] have set the conditions for the development of a highly chemo-and stereoselective aziridination of a,b-unsaturated aldehydes. [7] Central to the success of this approach was the ability of the organocatalyst to integrate orthogonal activation modes (iminium ion and enamine catalysis) into a more elaborate reaction sequence, [8] thus promoting first the nucleophilic addition of a N-centered nucleophile followed by an intramolecular cyclization (Scheme 1). We sought to extend this organocatalytic strategy to a,b-unsaturated ketones, an idea that was mainly triggered by the recent applications of chiral primary amine salts as efficient activators of enones through iminium catalysis.[9] The reduced steric constraints of primary amines offers the unique possibility of catalyzing processes between sterically demanding partners, overcoming the inherent difficulties of chiral secondary amine catalysis.In particular, we recently introduced the catalyst primary amine salt 1, [10] which is made by combining the easily available 9-amino(9-deoxy)epi-hydroquinine 2 with d-N-Boc phenylglycine (3; Boc = tert-butyloxycarbonyl). Salt 1 exhibits high reactivity and selectivity in the enantioselective conjugate additions of carbon-,[10a] oxygen-, [10b] and sulfurcentered [10c] nucleophiles to a,b-unsaturated ketones.To consolidate salt 1 as a general and selective iminium catalyst for enones, we questioned whether this catalytic system might be successfully extended to the highly enantioselective amine conjugate addition, a primary strategy for C À N bond construction. [11] Prompted by the s...

The first catalytic method for the asymmetric aziridination of cyclic enones is described. The presented organocatalytic strategy is based on the use of an easily available organocatalyst that is able to convert a wide range of cyclic enones into the desired aziridines with very high enantiomeric purity and good chemical yield. Such a method may very well open up new opportunities to stereoselectively prepare complex chiral molecules that possess an indane moiety, a framework that is found in a large number of bioactive and pharmaceutically important molecules.

The development of novel and efficient catalytic methodologies for the stereoselective preparation of chiral aziridines is an important synthetic target. [1] Aziridines constitute a key structural feature of several classes of natural products and are extremely versatile building blocks that can undergo synthetically useful transformations. [2] The catalytic asymmetric aziridinations of olefins provide direct and useful access to such a valuable scaffold, and great efforts and progress have been made in this field. [3] However, to our knowledge, a general and highly stereoselective aziridination of simple a,b-unsaturated enones is still lacking. [4,5] Herein, we report an organocatalytic solution to this synthetic problem that is founded upon the use of a readily available chiral primary amine catalyst salt as well as on a rationally designed N-centered nucleophile.Previously reported asymmetric aziridinations of enones have severe restrictions in scope, as only chalcones are suitable substrates: metal-based systems [4] can provide highly enantioenriched compounds protected as N-tosyl derivatives, a protecting group that can prove to be difficult to remove, whereas two ingenious organocatalytic entries to nonprotected aziridines, showing moderate enantioselectivity (up to 67 % ee), were recently reported through the use of chiral tertiary amines. [5] Recently, the spectacular advances achieved in the field of chiral secondary amine catalysis [6] have set the conditions for the development of a highly chemo-and stereoselective aziridination of a,b-unsaturated aldehydes. [7] Central to the success of this approach was the ability of the organocatalyst to integrate orthogonal activation modes (iminium ion and enamine catalysis) into a more elaborate reaction sequence, [8] thus promoting first the nucleophilic addition of a N-centered nucleophile followed by an intramolecular cyclization (Scheme 1). We sought to extend this organocatalytic strategy to a,b-unsaturated ketones, an idea that was mainly triggered by the recent applications of chiral primary amine salts as efficient activators of enones through iminium catalysis. [9] The reduced steric constraints of primary amines offers the unique possibility of catalyzing processes between sterically demanding partners, overcoming the inherent difficulties of chiral secondary amine catalysis.In particular, we recently introduced the catalyst primary amine salt 1, [10] which is made by combining the easily available 9-amino(9-deoxy)epi-hydroquinine 2 with d-N-Boc phenylglycine (3; Boc = tert-butyloxycarbonyl). Salt 1 exhibits high reactivity and selectivity in the enantioselective conjugate additions of carbon-, [10a] oxygen-, [10b] and sulfurcentered [10c] nucleophiles to a,b-unsaturated ketones.To consolidate salt 1 as a general and selective iminium catalyst for enones, we questioned whether this catalytic system might be successfully extended to the highly enantioselective amine conjugate addition, a primary strategy for C À N bond construction. [11] Prompted b...

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