Supramolecular Photochirogenesis with Carbenes Entrapped in Cyclodextrins

Abstract

Two achiral diazirines 1a and 1b have been encapsulated in the inherently chiral cavity of α-cyclodextrin (6-Cy), β-cyclodextrin (7-Cy) and permethylated β-cyclodextrin (TRIMEB) and photolyzed. Because of supramolecular photochirogenesis the generated carbenes afford intramolecular C-H insertion products not as a racemate but one enantiomer is slightly favored. With 1a@(6-Cy) 2 the ee of product 7a is doubled. To the best of our knowledge for the first time for carbene

Encapsulation of Reactive Intermediates

“…The aim of this study was to determine whether the intrinsically chiral cyclodextrin hosts are able to cause the formation of one enantiomer over the other. 63 The unsubstituted bicyclo[3.2.1]octan -8 -ylidene ( 91 ) reacts exclusively through 1,3 -CH insertion to tricyclooctane 92 . 64 For the 3 -endo -substituted carbenes 91 , a second reaction pathway becomes competitive yielding bicyclo [3.3.0]octene 93 by a 1,2 alkyl shift.…”

“…Also the formation of 93 is preferred over 92 . 63 For 90b @TRIMEB, a single crystal suitable for X -ray analysis could be grown ( Figure 10.6 ). 61 The structure obtained ascertains the complete separation of one guest molecule from another and explains why azine 94 is lacking in the product mixture resulting from the photolysis of 90b @TRIMEB.…”

Multigram Synthesis of Functionalized Spirocyclic Diazirines

“…steroid analogues such as 4 , Boc‐protected photo‐proline 5 , ), synthesis of spirocyclic diazirine‐containing building blocks is discussed in the literature to a lesser extent. The prominent role of spirocyclic diazirines in biomedical research,, , physical organic chemistry and organic synthesis, motivated us to challenge the synthesis of a series of diazirines derived from saturated carbo‐ and heterocycles with different ring size and substitution pattern. Since it was outlined that amide formation was the major reaction for diazirine photoaffinity labelling probes synthesis (43 % of the methods used), we have focused on the preparation of building blocks containing carboxylic acid and amine functions.…”

Carbenes and Nitrenes

“…55 A strong host effect has been observed on the reaction ee outcome but only very low enantioselectivities are obtained, the best one (8%) being achieved with the less flexible α-cyclodextrin.…”