Adamantane, chlorination

The synthesis begins with the halogenation of adamantane (74) with bromine to give 76 or chlorine and AlClg to give 75. The four bridgehead positions... 

Dimeric (Me2AuCl)2 has been used to close the cationic adamantane cage of a bowl-shaped iVV-donor ligand with a [m-Me2Au]+ unit. The two chlorine atoms are accommodated in the [m-Me2AuGl2] counterion (Equation (7)).34... 

CIS-[Ru(H20)2(dinso) ] is made from as-RuClj(dmso) and Ag(BF ) in aq. EtOH. The system c/s-[Ru(H20)j(dmso) ] Vaq. Na(ClO) or TBHP/CH Cl oxidised alkanes such as adamantane, cyclo-octane, -heptane and -hexane to the corresponding alcohols and ketones as did [Ru(Hj0) PWjj(0)3g ] . A free-radical mechanism may be involved for the TBHP oxidations, but those with (C10) probably involve oxoruthenate(VI) or oxoruthenate(IV) intermediates [823], The oxidative destruction of a-chlorinated alkenes by CM-[Ru(HjO)2(dmso) ] Vaq. Oxone /Me(CH3) jN(HSO ) MCj to carboxylic acids and ultimately to CO and HCl was reported [946],... 

Furthermore, di- and polychlorination are much less prevalent. Dicarboxylic acids are predominantly chlorinated in the middle of the chain,99 and adamantane and bicy-clo[2.2.2]octane at the bridgeheads100 by this procedure. The reasons for the high to - 1 specificity are not clearly understood.101 Alkyl bromides can be regioselectively chlorinated... 

Nitronium tetrafluoroborate in the presence of pyridine poly(hydrogen fluoride) (PPHF) can be used to substitute chlorine or bromine in adamantanes and other hydrocarbons (see Table 21).90... 

Improved yields of adamantane up to 65% were achieved by using superacidic systems [HF-SbF5, CF3S020H-B(0S02CF3)3, various solid superacids]40"42 and chlorinated Pt on alumina.43 More recently near-quantitative isomerization with conjugate superacids promoted by 1-haloadamantanes as the source of 1-ada-mantyl cation and sonication was reported.44... 

Selective monohalogenation (chlorination and bromination) can be accomplished with excess methylene halides in the presence of SbF5.535 Adamantane, for example, gives 1-chloroadamantane in 80% yield at ambient temperature in 24 h. 

The chlorination of adamantane by either antimony pentachloride or ferric chloride in carbon tetrachloride gives low (approximately 4) initial tertiary secondary product ratios. Attention was called to the similarity of these ratios to those of known radical processes 36°). 

The chemistry of adamantylidene adamantane has been found to be quite unusual, due primarily to the highly hindered character of the double bond in this system. Bromination of adamantylidene adamantane gave the first isolated bromonium ion 263). Chlorination gives similar results at low temperatures while at higher temperatures chlorine is found to enter the methylene positions of the adamantyl nucleus, presumably via a protoadamantene-like intermediate 364i. 

For electrophilic and more bulky radicals, for example CnHal2n+i, selectivity increases dramatically. Whereas the selectivity for the radical chlorination (Table 1, entry 7) and bromination (Table 1, entry 8) of adamantane with Hal2 in CC14 is only approximately 5, for chlorinations with CC14 (Table 1, entries 9 and 10) and brominations with BrCCl3 (Table 1, entry 11) the selectivity increases to 21.5-27. Halogenations under metal-catalyzed GIF conditions (Table 1, entry 12) or in the presence of dioxirane (Table 1, entry 13) are less selective, because of the participation of oxygen-centered (GIF) or methyl (DMD) radicals. 

Fig. 1.34. Chlorination of adamantane to furnish tert-adamantyl chloride (A) and sec-adamantyl chloride (B), using differents reagents. In the reaction with the A B selectivity amounts to 68 32 in carbon disulphide and 39 61 in carbon tetrachloride (each at 25°C). In the reaction with S02CI, in sulfolan the A B selectivity is > 97.5 2.5 (at 60°C). The formation of sec-adamantyl chloride (B) proceeds via the secondary radical C, tert-adamantyl chloride (A) is formed via the tertiary radical D.

At even higher pH values, metal catalysis is required for chlorination to proceed. Thus, at pH =11, nickel(salen) catalyzes the chlorination of adamantane, cyclohexane and toluene785 and manganese porphyrin promotes the chlorination of cyclohexane786. Selective side-chain chlorination by sodium hypochlorite under PTCs at pH = 8.5 has been used for benzylic chlorinations787,788 and for the functionalization of poly(4-methyl-styrene)789,790. Similarly, with calcium hypochlorite in acetic acid, ring chlorination is reported for toluene, xylenes, anisole and other activated aromatics791. 

AgSbF6/Cl2/CH2Cl2 at -IS to 4 3S C is reported to be a convenient and effective reagent for the electrophilic chlorination of tertiary alkanes and cycloalkanes. Adamantane was sufficiently reactive to undergo uncatalyzed electrophilic bromination at 80 Substrates with adjacent tertiary C—H bonds... 

Ionic chlorination of alkanes.6 Alkanes are readily chlorinated by sulfuryl chloride in sulfolane (I, 1144-1145 2, 402-403). Thus adamantane (1) is converted almost exclusively into 1-chloroadamantane (2). Norbomane is converted under these conditions exclusively into 2-cxo-chloronorbornanc. -Hexane is converted into 1-chloro-hexane (20%), 2-chlorohexane (56%), and 3-chlorohexane (24%). The chlorination proceeds by an ionic mechanism. 

Aromatic solvents and carbon disulfide often increase the chlorination selectivity due to the formation of n- or O-complexes between the solvent molecules and the chlorine atom. Such an interaction decreases the reactivity and hence increases the selectivity toward the hydrogen atoms. For example, photochlorination of adamantane (461) gives a higher production of 1-chloroadamantane in CS2 than in benzene (Scheme 6.221).1302... 

Selective chlorination. DCU when activated by light converts cyclohexane to chlorocyclohexane in high yield. The reagent also converts adamantane into 1-chloroadamantane. A more useful reaction is chlorination of steroids at Cq to give, after dehydrochlorination with AgClOi, 9(1 l)-dehydro derivatives (equation 1),... 

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)... 

A range of triflate derivatives of sila-adamantanes have been prepared from methylsilyladamantanes by cleaving the Si-Me bond with ICl/AgOTf These compounds have been used then as precursors to cationic sila-adamantanes <2002JOM(658)141>. Various C-chlorinated and C-brominated tetrasila-adamantanes have also been prepared and their chemistry explored <2000CJC1388, 1995BSF585>. 

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