A New Model of Light‐Powered Chiral Molecular Motor with Higher Speed of Rotation, Part 1 – Synthesis and Absolute Stereostructure

Abstract

To develop a molecular motor with a higher speed of rotation, a new model light-powered chiral molecular motor 2 of fivemembered ring type was designed, and the motor rotation isomers (-)-2a and (-)-2c were directly synthesized in enantiopure forms for the first time from the ketone (+)-8. The precursor alcohols 9 and 10 were enantioresolved by the camphorsultam-dichlorophthalic acid (CSDP acid; 3) method, and their absolute configurations were determined by X-ray crystallographic analysis of the CSDP ester (-)-11b and chemical correlations. The enantiopure ketone (S)-(+)-8

Determination of absolute configurations by X‐ray crystallography and 1H NMR anisotropy

“…2). [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] In this case, the absolute configuration of the point in question can be automatically determined using the chirality of the auxiliary introduced as an internal reference. Consequently, samples do not need to contain heavy atoms for anomalous dispersion effect.…”

Asymmetric Synthesis of First Generation Molecular Motors

“…8 The desired product 11 was obtained without racemization in 38% yield with an E / Z ratio of 40/60 in the case of ketone 2 . 8 More surprisingly, the product was obtained with an enantiomeric excess of >98% ee (for the E isomer), starting from 89% ee for ketone 2 . An amplification of enantiomeric purity in the McMurry coupling has, as far as we know, not been reported in the literature.…”

“…8 Using a combination of TiCl 3 and LiAlH 4 as the reductant, the desired product 11 was obtained without racemization. 8 The desired product 11 was obtained without racemization in 38% yield with an E / Z ratio of 40/60 in the case of ketone 2 . 8 More surprisingly, the product was obtained with an enantiomeric excess of >98% ee (for the E isomer), starting from 89% ee for ketone 2 .…”

The McMurry Coupling and Related Reactions

“…The coupling of chiral α-substituted ketones such as 31 using the TiCl 3 -LiAlH 4 system proceeds without epimerization. 127 The enantiomerically enriched enone 32 reacts with acetone in the presence of TiCl 4 -LiAlH 4 to furnish the tetrasubstituted alkene without double bond isomerization. 128 Of note, the treatment of enone 33 129 and dienone 34 83 with the TiCl 4 -Zn or Ti powder-TMSCl system results in the selective coupling of the unsaturated carbonyl groups.…”

“…263,264 The ten-membered-ring sesquiterpenes, bicyclogermacrene (125) 265 and its stereoisomer, lepidozene, 265,266 dihydrogermacrene, 267 and helminthogermacrene 268 are prepared through the low-valent titaniumpromoted cyclization. Eleven-membered ring formation by the intramolecular coupling of keto aldehydes is involved in the syntheses of the tricyclic trinervitane skeleton 126 269 and humulene (127). 270 Twelve-membered-ring formation is applied to the total synthesis of verticillene (128), a biogenetic precursor of taxane alkaloids.…”