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The synthesis and reactivity of tetracyclo [3.3.1.1³‧⁷.0¹‧³] decane

University of British Columbia

The structures and some properties of adamantane (1b), strained cyclopropanes (23), and certain small ring propeller-like molecules (28) are reviewed. The synthesis of a new type of compound containing a combination of such structures and properties is presented. This compound tetracyclo [3.3.1.1³‧⁷.0¹‧³] decane or more simply 1,3-dibromoadamantane (DHA) contains a very strained cyclopropyl group within an adamantane skeleton and was produced by bonding two bridgehead (tertiary) carbons together across the normally extremely rigid structure of adamantane. In the synthesis of DHA using alkali metal (or alloys) with 1,3-dibromoadamantane (37), the reaction times and relative yields of adamantane and DHA were extremely variable. The former difficulty was resolved by the addition of an initiator (usually ṯ-butyl alcohol), while the yields were increased and made consistent by substituting sodium naphthalide or ṉ-butyl lithium - hexamethylphosphoramide for the alkali metals. DHA and adamantane were also isolated as the major products from the reaction of 1,3,5-tri- and 1,3,5,7-tetrabromoadamantane with alkali metals or alloys. DHA is one of the few organic molecules which possesses a so-called inverted geometry about the internally bonded bridgehead (quaternary) carbons. Wiberg, Hiatt and Burgmaier⁵⁵ have defined an inverted carbon as one "in which all atoms joined to the bridgehead atoms (inverted carbons) lie in one hemisphere, (i.e. in one plane or on one side of a plane passing through the bridgehead atoms)." The inversion of the DHA bridgehead carbons results in a highly strained bond and an unusually great reactivity for a formally saturated hydrocarbon. DHA reacts spontaneously with oxygen at room temperature to give a peroxy polymer Ad - O ≁ O - Ad – O ≁[sub x] O-Ad which explodes at ca. 146°C. DHA also reacts rapidly with halogens, acids, and mercuric acetate to yield halides, esters and alcohols, alcohols is slow (more than 24 hr to complete), Lewis acid catalysts promoted rapid addition of both alcohols (to give ethers) and benzene (to give phenylated adamantanes). Adam's catalyst promoted the rapid (30 min) addition of hydrogen to DHA in n-heptane solution to produce adamantane. In the solid phase DHA polymerized readily at ca. 160°C to give a highly insoluble product, polyadamantane Ad-(Ad)[sub x] -Ad which possesses great thermal stability (decomposition point ca. 500°C under nitrogen). In ṉ-octane solution under nitrogen the half life of DHA was 4,45 hr at 195°C, The reaction of DHA with halogens in ether gives (3-halo-1-adamantanyl)-diethyl oxonium trihalide. The reaction of this unstable intermediate with nucleophiles, for example H₂O or NaCN, is discussed as a potential source of unsym-metrical 1,3-disubstituted adamantane derivatives.

Text

2010-02-05

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http://hdl.handle.net/2429/19715

Chemistry

University of British Columbia

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