The First Direct and Enantioselective Cross-Aldol Reaction of Aldehydes

The first enantioselective catalytic direct cross-aldol reaction that employs nonequivalent aldehydes has been accomplished using proline as the reaction catalyst. Structural variation in both the aldol donor (R_1 = Me, n-Bu, Bn, 91 to >99%) and aldol acceptor (R_2 = I-Pr, I-Bu, c-C6H11, Et, Ph, 97−99% ee) are possible while maintaining high reaction efficiency (75−88% yield). Significantly, this new aldol variant allows facile enantioselective access to a broad range of β-hydroxy aldehydes which are valuable intermediates in polyketide syntheses

Two-Step Synthesis of Carbohydrates by Selective Aldol Reactions

Studies of carbohydrates have been hampered by the lack of chemical strategies for the expeditious construction and coupling of differentially protected monosaccharides. Here, a synthetic route based on aldol coupling of three aldehydes is presented for the de novo production of polyol differentiated hexoses in only two chemical steps. The dimerization of α-oxyaldehydes, catalyzed by l-proline, is then followed by a tandem Mukaiyama aldol addition-cyclization step catalyzed by a Lewis acid. Differentially protected glucose, allose, and mannose stereoisomers can each be selected, in high yield and stereochemical purity, simply by changing the solvent and Lewis acid used. The reaction sequence also efficiently produces ^(13)C-labeled analogs, as well as structural variants such as 2-amino– and 2-thio–substituted derivatives

The First General Enantioselective Catalytic Diels−Alder Reaction with Simple α,β-Unsaturated Ketones

The first general approach to enantioselective catalysis of the Diels−Alder reaction with simple ketone dienophiles has been accomplished. The use of iminium catalysis has enabled enantioselective access to a fundamental Diels−Alder reaction variant that has previously been unavailable using chiral Lewis acid catalysis. A new chiral amine catalyst has been developed that allows a variety of monodentate cyclic and acyclic ketones to successfully participate in enantioselective [4 + 2] cycloadditions. A wide spectrum of cyclic and acyclic diene substrates can also be accommodated in this new organocatalytic transformation. A computational model is provided that is in accord with the sense of enantioinduction observed for all reactions conducted during the course of this study

On the locus formed by the maximum heights of projectile motion with air resistance

We present an analysis on the geometrical place formed by the set of maxima of the trajectories of a projectile launched in a media with linear drag. Such a place, the locus of apexes, is written in term of the Lambert $W$ function in polar coordinates, confirming the special role played by this function in the problem. In order to characterize the locus, a study of its curvature is presented in two parameterizations, in terms of the launch angle and in the polar one. The angles of maximum curvature are compared with other important angles in the projectile problem. As an addendum, we find that the synchronous curve in this problem is a circle as in the drag-free case.Comment: 7 pages, 6 color eps figures. Synchronous curve added. Typos and style corrected

Miriam MacMillan Correspondence

Entries include a typed biographical letter on personal stationery