A General and Nonempirical Approach to the Determination of the Absolute Configuration of 1-Aryl-1,2-diols

Abstract

We describe herein a simple, general, and reliable nonempirical approach, based on the exciton coupling method, to assign the absolute configuration of the benzylic stereogenic center of 1-aryl-1,2-diols. According to this method, it is only necessary to prepare the 4-biphenylboronic esters of the diols and to record their CD spectra in the 230-300 nm range, i.e., in the range corresponding to the long-axis (1)L(a) transition of the biphenyl chromophore. From the sign of the CD couplet or Cotton effect at 260 nm it is possible to know the chirality defined by the aryl and biphenyl chromophore transitions and then to determine the absolute configuration of the benzylic carbon. By this approach, simple rules have been formulated which allow us to establish the absolute configuration of many classes of 1-aryl-1,2-diols.

Pyriculins A and B, two monosubstituted hex‐4‐ene‐2,3‐diols and other phytotoxic metabolites produced by Pyricularia grisea isolated from buffelgrass (Cenchrus ciliaris)

“…To establish this last piece of information, we resorted to derivatization of compound 1 with phenylboronic acid to transform it into the corresponding cyclic boronate diester or dioxaborolane ( 1a , Figure ). In this way, we aimed at reducing the conformational freedom and inserting a second phenyl chromophore capable of giving exciton‐coupled ECD spectra by interacting with the preexisting chromophore …”

EXAT: EXcitonic analysis tool

“…[7][8][9][10] To relate the CD spectrum of chirally arranged chromophores with their structure, and determine their absolute configurations, the so-called exciton chirality method (ECM) has been widely and successfully used. [11][12][13][14][15] The application of the ECM to dimeric systems results in a simple chirality rule, which relates the sign of the CD Cotton effect to the sense of twist between the transition dipole moments of the two chromophores. [2,4,16,17] However, in more complex cases, where many transitions are coupled, the interpretation of CD signatures is less straightforward.…”

An Electrophilic Cleavage Procedure for the Asymmetric Dihydroxylation: Direct Enantioselective Synthesis of Cyclic Boronic Esters from Olefins

“…The example of 4-biphenyl boronic acid (entry 4) is particularly noteworthy, since it allows for direct access to the respective chiral boronic esters, which are important derivatives for determination of absolute configuration of diols by means of circular dichroism spectroscopic analysis. [17] Mechanistic discussion: It has been a common feature in all dihydroxylation protocols established so far [1,3] that removal of the diol entity from the intermediate osma(vi) glycolate represents the decisive step for catalyst regeneration. This is usually accomplished through the hydrolytic cleavage of the osmium-oxygen bonds (Figure 2, left).…”