Optically active five-membered cyclic

Optically active five- or six-membered cyclic A -acyliminium ions of this type are generated from the a-inethoxy derivatives, easily obtainable through anodic methoxylation of intermediates that are prepared via ex-chiral-pool syntheses from certain natural amino acids. Reaction of 5-substituted five-membered cyclic A -acyliminium ions with various nucleophiles leads to the predominant formation of cw-products with moderate selectivity. The trans-selective reaction with alkyl copper reagents appears to be an exception. 

Our main example of enolate reactions in five-membered rings is one of some general importance. It illustrates how stereochemical information can be transmitted across a ring even though the original source of that information may be lost during the reaction. That may sound mysterious, but all will become clear. The first reaction is to make a five-membered cyclic acetal from an optically active hydroxy-acid. Our example shows (S)-(+)-niandelic acid reacting with t-BuCHO. 

Extraction equilibrium data are summarized in TABLE IV, together with the reported values of diameter and heat of hydration of alkali and alkaline earth metal cations. The ten-membered cyclic dimer extracted neither monovalent cations nor divalent cations above a detectable limit. On the contrary, the twenty-membered cyclic tetramer and the twenty -five-membered cyclic pentamer bound, more or less, monovalent and divalent cations, the latter showing somewhat higher Kg values than the former for any ions examined. No significant difference in ion extraction ability between racemic and optically active cyclic oligomers was observed. 

Unlike epoxides, these five-membered heterocyclics have received scant attention from organic chemists. But the recent catalytic asymmetric dihydroxylation of alkenes (14, 237-239), which is now widely applicable (this volume), and the ready access to optically active natural 1,2-diols has led to study of these compounds, including a convenient method for synthesis. They are now generally available by reaction of a 1,2-diol with thionyl chloride to form a cyclic sulfite of a 1,2-diol, which is then oxidized in the same flask by the Sharpless catalytic Ru04 system, as shown in equation I.1... 

However, even the a-unsubstituted y- and -alkenyl oximes readily give the corresponding five-and six-membered cyclic nitrones when the alkene is activated by a terminal ester group. For example, the bicyclic nitrone 4 was obtained with moderate diastereoselectivity from 3 via the oxime formed in situ1. From the optically active menthyl esters 5,1 1 mixtures of diastereomer-ic nitrones 6 were obtained. 

Preparation of cyclic ethers by intramolecular reactions of the primary (29 and 33) and the secondary alcohols (31 and 35) proceeds more easily using CS2CO3 or K3PO4, and binaphthyl-based monophosphine ligands VI-1, VI-9 [9], The five-, six-, and seven-membered cyclic ethers 30, 32, and 34 were prepared from the aryl chloride 31 and bromides 29 and 33. The benzoxazapine 36 was obtained without racemization of chiral alcohol by the cyclization of the optically active bromo alcohol 35. 

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