Adamantane formylation

Protonation of formic acid similarly leads, after the formation at low temperature of the parent carboxonium ion, to the formyl cation. The persistent formyl cation was observed by high-pressure NMR only recently (Horvath and Gladysz). An equilibrium with diprotonated carbon monoxide causing rapid exchange can be involved, which also explains the observed high reactivity of carbon monoxide in supera-cidic media. Not only aromatic but also saturated hydrocarbons (such as isoalkanes and adamantanes) can be readily formylated. 

While studying the reaction of adamantane with carbon monoxide under super-acidic catalysis, formylation (formation of 1-adamantanecarboxaldehyde) was found by Olah and co-workers447 to effectively compete with Koch—Haaf carboxylation (formation of 1-adamantanecarboxylie acid, major product formed in 60-75% yield). On the basis of results acquired by the reaction of 1,3,5,7-tetradeuteroadamantane, formylation was interpreted by insertion of the formyl cation into the tertiary C—H cr-bond [Eq. (5.163)]. 

Adamantan 2-(Formyl-methylen)-E19c, 199 (aus 2-Ethinyl-2-hydroxy-adamantan)... 

Zuweilen mlissen die Versuchsbedingungen drastisch verscharft werden (z. B. bei der Her-stellung von Formyl-adamantan)332. 

Treatment of N(9)-formyl-9-azabicyclo[3.3.1]nona-2,6-diene (42) with bromine in methanolic KOH-solution gave N(6)-formyl-4 8 f )-dibromo-2-oxa-6-aza-ada-mantane (43) in 56% yield. Subsequent LiAlH4-reduction gave 81% of unsubstituted N(6)-methyl-2-oxa-6-aza-adamantane (40) ... 

Transannular addition of sulfur dichloride to 9-azabicyclo[3.3.1]nona-2,6-dienes (42 N-formyl 9l 44 N-phenylsulfonyl 94 and 62 N-tolylsulfonyl p 3i, 32)j applied as an entry to the 2-thia-6-aza-adamantane system. The chlorine atoms in 91 were easily exchangeable with sodium iodide in boiling diethyl ketone (-> 92, 82%)" or with silver acetate in acetic acid (- 93, 70%)" resp. Under analogous reaction conditions the dichloride 94 was transformed into the diacetate 95 (95%) " LiAlH4-reduction of the diacetate 93 yielded 74% of N(6)-methyl-4 8 -dihydroxy-2-thia-6-aza-adamantane (97). The C(4) and C(8)... 

Using N(6)-formyl-4 1,8 1 1-dichloro-2-thia-6 -aza-adamantane 91) as starting material, reaction with sodium iodide in diethyl ketone yielded 82% of the diiodide 92 (episulfonium ion) and reaction with silver acetate in acetic acid gave 69% of the diacetate 93 (episulfonium ion) (2.1.9.) Under analogous conditions the dichloride 94 was transformed to the diacetate 95 (95%) (2.1.9.) ... 

Esr investigation of bicyclo[3.2.0]heptenyl radicals and 7-norbornadienyl radicals in an adamantane matrix which prevents combination and disproportionation reactions allows the observation of interesting processes forbidden in solution because of their high activation barrier using keto or formyl precursors, interesting behavior of the acyl radicals has been observed, including the reversible intramolecular addition to Cy 4 in the Cy4/Cy5 case. ... 

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