Hydrogen bonding and solvent effects in heteroaryldi(1-adamantyl)methanols: an NMR and IR spectroscopic study

Reaction of the organolithium derivatives of certain heteroaromatics [2-fur anyl, 2-thienyl, 2-thiazolyl, 2-pyridyl and 2-(3-methylpyridyl)] with di(1- adamantyl) ketone gives potentially rotameric tertiary alcohols. With 2-pyr idyl- and 2-(3-methylpyridyl)lithium only the syn isomer is obtained. The s yn isomer makes up 85-100% of (2-furanyl)diadamantylmethanol and 80-90% of the 2-thienyl derivative, depending on the NMR solvent. In chloroform or be nzene the 2-thiazolyl derivative is a 2: 1 mixture, the isomer with the sul fur atom syn to the OH group predominating; in DMSO or in the solid state t his is the sole species. The IR absorption frequency for OH stretching corr elates with the corresponding proton NMR shift in chloroform and with its t emperature dependence, Delta delta/Delta T. In pyridine Delta delta/Delta T is either large (-20 ppb/degrees C) or small (-1 to -2 ppb/degrees C) for intermolecular and intramolecular hydrogen-bonded species, respectively. Se mi-empirical calculations (AMI and PM3) suggest that the anti alcohols shou ld be the more stable in the gas phase, but solvent effects and hydrogen bo nding, in the case of the pyridyl derivatives, appear to reverse this situa tion, making the isomer with OH syn to the heteroatom the principal, and so metimes the only, species observed in solution.