2-amino-2-ethynyladamantane

Phosphorus tribromide (3.1ml, 8.91g, 32.1mmol) and a trace of pyridine (4 drops) were slowly added to 2-(trimethylsilylethynyl)-admant-2-ol (2.94g, 11.85mmol) dissolved with 80ml dry ether to give a white suspension that was stirred at roomtemperature under nitrogen for 46h. The now yellow solution was slowly poured onto ice cold dilute hydrochloric acid, and usual work-up afforded 3.1g (84%, 9.9mmol) of a yellow oil which upon TLC and IR analysis was found to consist of 2 isomers. IR : 2919.8, 2164.1 (C[[equivalence]]C, st), 1937.2 (C=C=C, st), 1596.4 (C=C, st), 841.0 (-TMS) cm^-1.

However, boiling under reflux (160^oC) for 1h in DMF nearly totally shifted the equilibrium of the two isomers towards the ethynyl compound (15). IR : 2926.0, 2164.1, 1687.4, 854.0 cm^-1. The yellow oil was diluted with 80ml ethanol and slowly added to a saturated solution of ammonia in ethanol before stirring for 67h at roomtemperature. To complete the reaction, gaseous ammonia was bubbled through the to 60^oC warmed solution for 4h. Basic work-up gave 1.4g (48%) of a yellow oil which contained at least 3 different substances (TLC: hexane/ether/ethylacetate/petrol =17.5:5:2.5:2.5). Desilylation in 20ml methanol containing excess potassium hydroxide at reflux for 1h gave a yellow oil consisting of 4 compounds, of which the one with RF=0.5 (hexane/ether/ethylacetate/ petrol =17.5:5:2.5:2.5) turned out to be 2-amino-2-ethynyl-adamantane 5 with 15% yield (0.31g). Crystals suitable for X-ray analysis were grown with the slow evaporation method.