L*Adamantanol

Protoadamantanone has been prepared by the nitrous acid deamination of 2-amino-l-adamantanol (77%), by aprotic diazo-tization of endo-7-aminomethylbicyclo[3.3.1]nonan-3-one in benzene with an equivalent amount of acetic acid (67%), and by thermolysis of 1-adamantyl hypohalites followed by base-promoted cyclization of the resulting halo ketones (32-37%)." In spite of low and erratic yields, the last reaction sequence has provided the most convenient route to the protoadamantanes, since the other two approaches require lengthy syntheses of the starting materials. 

Carbonylation-oxidation of the THF complexes (S)-58 and (R)-58 afforded the optically active (3 )-(+)-2-methyl-l-adamantanol (3)-60 and (R)-(—)-2-methyl-l-adamantanol (R)-60, respectively (Scheme 24) <2003MC121, B-2003MI97>. 

The rearrangements of several twistane derivatives to adamantyl cations under the same conditions, on the other hand, appear to involve reversible, random carbonium ion formation, at least to a limited extent. Rearrangement of 2-twistanol-2-d (38) occurs with considerable intermolecular hydrogen scrambling (Eq. (15)) 40T Similar intermolecular rearrangements are observed when a 50 50 mixture of 1-adamantanol and l-adamantanol-3,5,7-d3 in S02 is treated with SbFs 40). 

The reaction is conducted in 80-100% sulfuric acid and is greatly accelerated by BF3. Norbornene (1) is converted in good yield into ejco-norbornylacetic acid (2), and l-adamantanol (3) affords 1-adamantylacetic acid. 

Kinetic isotope effect of cyclohexanol formation. l-adamantanol/(2-adamantanol + 2-adamantanone) corrected for the number of C-H bonds in a group. 

Adamantyl iodide reacts with [Co(CN)j] to form [(l-adamantyl)Co -(CN)j] which was isolated as its potassium salt. The anion s stability in neutral or alkaline solution is comparable with that of [MeCo(CN)j] however, it undergoes facile acid-catalysed decomposition to 1-adamantyl cyanide and l-adamantanol. (7i-Cp)Co(PPh3)l2 reacts with cyanide to form [(7c-Cp)Co(PPh3)(CN)2], whereas a similar reaction of [(7i-Cp)Co(CO)l2] gives [(7i-Cp)Co(CN)3] . Alkylation of the anion yields [(7i-Cp)Co(CN)2-(CNMe)] or [(7 -Cp)Co(CNEt)3]2 +. 2o... 

Tertiary alcohols (6, 440). The detailed preparation of l adamantanol by livwith ozone adsorbed on silica gel has been sub-nulled lo Organic Syntheses. In addition to l-udainanlanol (93% yield), adaman-l.iiiv 1.3 diol aiul adainaiiiaiioiic are formed in minor amounis. ... 

Another feature of systems that are subject to B-strain is their reluctance to form strained substitution products. The cationic intermediates usually escape to elimination products in preference to capture by a nucleophile. Rearrangements are also common. 2-Methyl-2-adamantyl p-nitrobenzoate gives 82% methyleneadamantane by elimination and 18% 2-methyl-2-adamantanol by substitution in aqueous acetone. Elimination accounts for 95% of the product from 2-neopentyl-2-adaman l p-nitrobenzoate. The major product (83%) from 2-r-butyl-2-adamantyl p-nitrobenzoate is the rearranged alkene 5. 

This dry ozonation procedure is a general method for hydrox-ylation of tertiary carbon atoms in saturated compounds (Table 1). The substitution reaction occurs with predominant retention of configuration. Thus cis-decalin gives the cis-l-decalol, whereas cis- and frans-l,4-dimethylcyclohexane afford cis- and trans-1,4-dimethylcyclohexanol, respectively. The amount of epimeric alcohol formed in these ozonation reactions is usually less than 1%. The tertiary alcohols may be further oxidized to diols by repeating the ozonation however, the yields in these reactions are poorer. For instance, 1-adamantanol is oxidized to 1,3-adamantane-diol in 43% yield. Secondary alcohols are converted to the corresponding ketone. This method has been employed for the hydroxylation of tertiary positions in saturated acetates and bromides. 

Laali et al.234 have developed a method to the highly selective pura-adamantylation of arenes (toluene, ethylbenzene, anisole) with haloadamantanes (1-chloro- and 1-bromoadamantane, l-bromo-3,5,7-trimethyladamantane) and 1-adamantanol promoted by triflic acid in butylmethylimidazolium triflate [BMIM][OTf] ionic liquid. In contrast to reactions mn in 1,2-dichloroethane, little or no adamantane byproduct was detected in [BMIM][OTf. Furthermore, no isomerization of para-tolyladamantane was observed supporting the intramolecular nature of the formation of meta isomers. In competitive experiments with benzene-toluene mixture (1 1 molar ratio), high substrate selectivities were found (kT/kB = 16-17) irrespective of the alkylating agent. This is in sharp contrast to values about unity measured in 1,2-dichloroethane. 

The high yields and mild reaction conditions of each of these rearrangements to adamantane or 1-adamantanol constrast sharply with the low yields and relative severe reaction conditions required for the conversion of tetra-hydrodicyclopentadiene (2) to adamantane (l)4,4[Pg.16]

The precise mechanism of these intermolecular reactions is not known. Transient disproportionation processes, although well documented in less acidic media (see below and Section V.A.l), seem unlikely if alkyl cations alone are involved. Two possible explanations for the observed results may be considered. Small amounts of polymeric impurities may be present in the reaction mixture which could serve as a hydride source, catalyzing the intermolecular reaction as indicated in Eq. (16)4°). Alternatively, the intermolecular reactions may result from inefficient mixing during reaction initiation. In this case, unionized alcohols would serve as the hydride source. This latter alternative is consistent with the observation 4°1 that the deuterium in the 1-adamantanol obtained from the rearrangement of 38 is distributed between bridgehead and methylene positions. Unless more than one re-... 

Similar results are obtained with 2-adamantanol which rearranges to 1 -ada-mantanol (> 98 %) at 28°C in sulfuric acid. An equilibrium mixture containing small amounts of 2-adamantanol is rapidly achieved fromeither direction67 6 K This isomerization is one of the mechanistic bases for the preparation of ada-mantanone by the reaction of adamantane with sulfuric acid at 77°C (see Section V.A.l) 57> 67> 691. The Koch-Haaf carboxylation of 2-adamantanol similarly results in predominant 1-adamantyl carboxylic acid formation unless highly dilute reaction conditions are employed 57> 7°). 

Addition of methyl Grignard to 4-protoadamantanone gives a 2 1 mixture of 4-methyl-ejco-4-protoadamantanol and the corresponding encfo-epimer76). This mixture rearranges nearly quantitatively to l-methyl-2-adamantanol when treated with acid 76). 

Disubstituted adamantanes are most frequently obtained from internal cyclization reactions of a bridgehead substituent. Thus, photolysis of the azido-formate 79 gives 80 by nitrene insertion 279). 80 may be readily hydrolyzed to 2-amino-1-adamantanol (81) 75 Subsequent oxidation gives l-hydroxy-2-ada-mantanone (82) from which other derivatives may be prepared 280>2S1). An analogous carbene insertion is initiated by the thermal decomposition of the... 

The transesterification with secondary alcohols was also reported by the same group [72], By utilizing l,3-dicydohexyl-imidazolin-2-ylidene (ICy, 11) as catalyst, various alcohols 87 (including aliphatic cyclic and aromatic alcohols) reacted with diverse esters 88 to yield the desired esters 89 (Scheme 9.26). The steric bulk at the a position of the alcohol reduces the reaction rates, and longer reaction times are required hence, the reaction proceeds slowly (5 days) with tertiary alcohols (1-adamantanol) and requires higher catalyst loadings (20 mol%) to yield moderate yields (54%). 

Phenyl-2-adamantanamine, 60, 105 2-PHENYL-2-ADAMANTANAM1NE HYDROCHLORIDE, 60, 104 2-Phenyl-2-adamantanol, 60, 105 Phenylchlorodiazirine, 60, 55 PHENYL CYANATE, 61, 35 l-Phenyl-2,2-diethoxycyclopropane, 60, 8 Phenylmercuric acetate, 61, 82... 

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