Cycloadditions dictamnol

The metal-catalyzed [5 + 2]-cycloaddition of tethered VCPs and 7r-systems has been applied to the total syntheses of (-l-)-dictamnol,52 (+)-aphanomol l,53 and tremulenolide A.54 The tricyclic core of cyathane diterpenes such as (-l-)-allocyathin B25S and the tricyclic carbon skeleton of polyhydroazulenes such as dolatriol56 were also synthesized... 

Dicobalt octacarbonyl, in Pauson—Khand reaction homogeneous catalysis, 11, 340 metal-coupled promoters, 11, 339 non-oxidative promoter-assisted, 11, 338 oxidative promoter-assisted, 11, 337 physical promoters, 11, 339 solid-supported promoters, 11, 339 Dicobalt triple-decker sandwiches, preparation, 3, 14 (+)-Dictamnol, via [5+2]-cycloadditions, 10, 613-614 Dicyclohexylborane, for alkene hydroboration, 9, 150... 

Given the previously discussed examples of the [S-(-2] cycloaddition, one can imagine a variety of approaches to the synthesis of molecules like dictamnol. One which has found success is given in Scheme 8. The cycloaddition precursor is prepared in three steps fi om commercially available cyclopropanecarboxaldehyde. Cycloaddition of alcohol 68 proceeds in 69% yield to provide cycloadduct 70. The yield of the cycloaddition is improved to 80% by protecting the alcohol as a TBS ether (69), although the combined yield for cycloaddition and deprotection is 70%. With two additional steps from 70, dictanuiol (71a) was prepared in 10% overall yield, marking the first application of the metal-catalyzed [5+2] cycloaddition in natural product synthesis. 

Cycloaddition reactions of cyclopropanes via cleavage of the C—C bond have been apphed to the synthesis of a wide variety of natural products, particularly terpenoids. For example, (-H)-dictamnol [5], (-H)-aphanamol I [6], (-H)-tremulenolide A [7], and (-l-)-lirondosin A [8] were synthesized through a [5-h2] cycloaddition reaction of vinylcyclopropanes with C—C unsaturated bonds. ( )-Hirsutene [9], ( )-pentalenene [10], ( )-asterisca-3(15),6-diene [10], ( )-hirsutic acid [11], and (-l-)-asteriscanohde [12] were synthesized via rhodium(l)-catalyzed [5-H2-H1] cycloaddition of vinylcyclopropanes with alkenes and carbon monoxide. Total syntheses of ( )-a-agarofuran [13], and ( )-pyrovellerolactone [14] were also achieved through cycloaddition reactions of cyclopropane derivatives. For these syntheses, reference to the papers should be made directly. 

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