Cubyl iodides

The conversion of cubyl iodides into cubyl triflates has considerable interest since it permits further functionalization of these otherwise unreactive substrates. The use of IOB and trimethylsilyl triflate was a good approach to this problem (see also Section 7.4.4). 

A mixture of cubyl iodide (1 mmol), IOB (3 mmol) and trimethylsilyl triflate (666 mg, 3 mmol) in dry dichloromethane was stirred at room temperature for 1 h to several days, depending on the substituent X the following order was noted, concerning reaction time H < Me < C02Me < Br,I,Cl. After the usual work up, the residues were purified by flash chromatography (with pentane) or microdistillation to give the pure products in 50-60% yield. 

A solution or suspension of the acid (1 mmol) in carbon tetrachloride (75 ml) containing DIB (0.55 mmol) and iodine (0.5 mmol) was irradiated with two 100 W tungsten-filament lamps for 45 min at reflux temperature. Another portion of DIB (0.55 mmol) was then added and irradiation was continued for 45 min at reflux. The reaction mixture was washed with dilute sodium thiosulphate and water, concentrated and chromatographed (silica gel column, 9 1 hexanes-ethyl acetate) to afford the alkyl iodide. Several steroidal acids with the carboxyl group attached at a 1° or 2° carbon atom gave the corresponding iodides in good yields. Acids with a 3° a-C instead of the iodide afforded alkenes similarly, alkenes were formed with a fivefold excess of DIB in the presence of cupric acetate. Aromatic acids also underwent iododecarboxylation, in moderate yields very effective was the otherwise difficult transformation of 1,8-naphthalenedicarboxylic acid to 1,8-diiodonaphthalene (80%) [68]. Cubyl and homocubyl iodides were also prepared in excellent yield [69]. 

Photolysis of 1,4-diiodocubane (494) in nucleophilic solvents, such as methanol, was found to provide effectively the substitution product 495 (Scheme 6.241).1348 It was argued that the reaction proceeds via the formation of a caged radical pair and electron transfer to give iodide ion and a carbocation, which is trapped by the solvent (SN1 pathway). Hyperconjugative stabilization in cubyl cation cannot assist much from an extremely strained olefin cubene. However, the authors expected that photochemical fission of the C—I bond would still provide sufficient energy for production of the cation intermediate. 

---