Rotation barriers in aryl- and heteroaryldi(1-adamantyl)methyl systems; the ionic hydrogenation of heteroaryldi(1-adamantyl)methanols

Iridium-catalyzed borylation of thiophenes: versatile, synthetic elaboration founded on selective C–H functionalization

“…The two most common approaches are (i) electrophilic substitutions that are selective for 5-substitution when the 3-substituent is electron withdrawing and/or the electrophile is sterically hindered, 45,46 and (ii) directed ortho metalations (DoMs) where the 3-substituent is a poor directed metalation group (DMG). [47][48][49] When compared to DoMs, the selectivities for entries 2, 3, 5, and 6, are atypical. Even with relatively poor DMGs like Cl or Br at C-3, DoM at C-2 for thiophenes is often favoured.…”

Competing inter- and intramolecular hydrogen bonding: solvent-driven rotamerization in 3,4-(ethylenedioxy)-2-thienyldi(tert-alkyl)methanols

“…Aryl-and heteroaryldi(tert-alkyl)methanols exist in two rotameric forms which can be distinguished on the NMR timescale and can in some cases, particularly when the tert-alkyl group is a bulky substituent, such as 1-adamantyl, be separated by column chromatography. 1- 3 To date, however, when there is an alkoxy group close to the OH group, as in 2-anisyl-and 3-alkoxy-2-thienyldi(1-adamantyl)methanols, only the intramolecularly hydrogen-bonded rotamer has been found. 4, 5 The existence of the hydrogen bond and favourable steric effects would appear to be an adequate explanation for this phenomenon.…”

Rate and equilibrium effects of tert-alkyl groups on rotamerization in 3,4-alkylenedioxy-, 3-alkoxy- and 3,4-dialkoxy-2-thienyl(di-tert-alkyl)methanols: an IR, NMR, kinetics and MM studyElectronic supplementary information (ESI) available: additional experimental data. See http://www.rsc.org/suppdata/p2/b2/b203714a/

“…All new alcohols 4 (n = 1 and 4), 7 (n = 1, 3 and 4), 5 and 8 (R = Me, Et and i-Pr), 6 and 9 (R = Me and Et) were prepared by lithiation of the 3-alkoxy-, 3,4-dialkoxy-or 3,4-alkylenedioxythiophene by means of n-butyllithium-TMEDA in diethyl ether at room temperature, 1 followed by reaction with (1-adamantyl)(tert-butyl) ketone (4)(5)(6) or di-1-adamantyl ketone (7)(8)(9).…”

“…It will be remarked also that the barrier for 7 (n = 1) is very close to that for 2-thienyl-(di-1-adamantyl)methanol in DMSO at 350-420 K (21.1 kcal mol Ϫ1 ). 7 The rotation barriers are considerably enhanced by replacing tert-butyl groups by 1-adamantyl, the syn anti barrier being increased by 3.3 (3,4-methylenedioxythienyl) to 7.3 (3-isopropoxythienyl) kcal mol Ϫ1 on going from di-tert-butyl to di-1adamantyl. It is interesting to note that the barriers are not only greater but that the magnitude of the increase depends on the bulk of the substituted thiophene moiety.…”