Dihetero-adamantanes

Restriction among the great number of possible dihetero-tricyclodecanes to such with a carbocyclic 8-membered ring (cyclooctane) as basic skeleton, which is crosswise bridged by two heteroatoms, and restriction to 5-, 6- and 7-membered heterocyclic rings, isomeric dihetero-tricyclodecanes of the following five different stmctural types are possible 2,6-dihetero-adamantane (G 7 ) 2,7-dihetero-isotwistane (G 2,7-dihetero-twistane (G S) 2,8-dihetero-homotwistbrendane (G 4) and 2,6-dihetero-tricyclo[3.3.2.0 Jdecane (G 5) . 

This review summarizes the results on dihetero-tricyclodecanes of the types G1 -G 5 known at present with particular emphasis on the synthesis of compounds from suitable 9-heterobicyclo[3.3,l ]- and 9-heterobicyclo[4.2.1 Jnonanes as well as by molecular rearrangements of dihetero-tricyclodecanes involving neighboring group participation. Furthermore spectral data are discussed mainly in connection with structural assignments. 

Hexamethylenetetramine (urotropine) was not only the first but also for many years also the sole compound whose adamantane structure (tricyclo[3.3.1.1 Jdecane) was a certainty. Interestingly, hexamethylenetetramine was also the first organic compound whose structure was determined by X-Ray in 1923  

Pure carbocyclic adamantane [G 1 X(2) = CH2, Y(6) = CH2] was first isolated in 1933 by Landa and Machacek from a high boiling petroleum fraction. Its structure was proved by a sophisticated, although laborious,synthesis by Prelog and Seiwerth in 1941. In spite of some improvements of the original procedure the synthesis of larger amounts of adamantane remained difficult. In a first attractive 

Adamantanes in which one or several of the methylene groups or one or several of the bridgehead carbonatoms are replaced by heteroatoms have been (with the exception of hexamethylenetetramine) subjects of intensive interest for about 20 years only. 

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Of the many possible general pathways the following five A—E have already been successfully applied to the synthesis of 2,6-dihetero-adamantanes. They use either... 

By the approach B Stetter and coworkers successfully synthesized in 1966 the first 2,6-dihetero-adamantane, the 2,6-dioxa-adamantane (14). Oxymercuration of... 

Disubstituted 2,6-Dihetero-adamantanes The methylene groups H2—C(9) and Hj—C(10) in 4,8-disubstituted 2,6-dihetero-adamantanes appear generally independent of the nature of X and Y... 

In this section several characteristic NMR-data of 2-oxa-6-aza-adamantanes [X(2) = O, Y(6) = NR] diall be discussed standing as typical examples for the rather large number of 4,8-disubstituted 2,6-dihetero-adamantanes known so far. 

In the series of dihetero-tricyclodecanes, substitutions and rearrangements involving neighboring group participation of heteroatoms (onium ions) especially of oxygen (oxonium ions) sulfur (episulfonium ions, thiiranium ions) and nitrogen (ammonium ions, aziridinium ions) as well as in one case also of selenium (epi-selenium ions), were studied on adamantanes (G1), isotwistanes (G 2), twistanes (G 2) and homotwistbrendanes (G 4). 

Starting from dihetero-tricyclodecanes described in the Sections 2. and 3. of the types of adamantane G1), isotwistane (G 2), twistane (G 3) and homotwistbrendane (G 4), which in their turn were prepared either by cyclization of suitable 9-heterobicyclo-... 

For tricyclo[4.3.1.0 ]decane the following trivial names were introduced in the literature isoadamantane (1968) protoadamantane (1968) isotwistane (1969) and 2(3 - 4)abeo-adamantane (1970) In the present review the name isotwistane will be applied, which until now is exclusively used to describe such 2,7-dihetero-tricyclodecanes. However, one should pay attention to the fact that since 1972 the trivial name iso-twistane is also applied for tricyclo[4.3.1.0 )decanes. 

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