On the regioselectivity and diastereoselectivity of ACC hydrazone alkylation

Synthesis of All Stereoisomers of RK460 and Evaluation of Their Activity and Selectivity as Abscisic Acid Receptor Antagonists

The PYR/PYL/RCAR protein families have recently emerged as receptors of the phytohormone abscisic acid (ABA, 1), which regulates plant responses to environmental stress. These families have multiple members with different physiological actions, and so selective agonists or antagonists are needed both as tools to elucidate functional differences and as lead compounds for agrochemicals. We previously identified RK460 (rac-3 a) as a PYR1-selective antagonist, and showed that it possesses five stereocenters on a 6,5-cis-bicyclo skeleton. Here, we synthesized all the stereoisomers of RK460 and evaluated their activity towards a panel of receptors. Relative stereochemistry as well as absolute stereochemistry was important for selective action.

Formation, Alkylation, and Hydrolysis of Chiral Nonracemic N-Amino Cyclic Carbamate Hydrazones: An Approach to the Enantioselective α-Alkylation of Ketones

The α-alkylation of ketones is a fundamental synthetic transformation. The development of asymmetric variants of this reaction is important given that numerous natural products, drugs, and related compounds exist as α-functionalized ketones or derivatives thereof. We previously reported our preliminary studies on the development of a new enantioselective ketone α-alkylation procedure using N-amino cyclic carbamate (ACC) auxiliaries. In comparison to other auxiliary-based methods, ACC alkylation offers a number of advantages and is both highly enantioselective and high yielding. Herein, we provide a full account of our studies on the enantioselective ACC ketone α-alkylation method.

Direct Asymmetric Alkylation of Ketones: Still Unconquered

The alkylation of ketones is taught at basic undergraduate level. In many cases this transformation leads to the formation of a new stereogenic center. However, the apparent simplicity of the transformation is belied by a number of problems. So much so, that a general method for the direct asymmetric alkylation of ketones remains an unmet target. Despite the advancement of organocatalysis and transition-metal catalysis, neither field has provided an adequate solution. Indeed, even use of an efficient and general stoichiometric chiral reagent has yet to be reported. Herein we describe the state-of-the-art in terms of direct alkylation reactions of some carbonyl groups. We outline the limited progress that has been made with ketones, and potential routes towards ultimately achieving a widely applicable methodology for the asymmetric alkylation of ketones.