Three-Component Intramolecular Two-Alkyne Annulations of Fischer Carbene Complexes: New Strategies for Steroid Synthesis (original) (raw)
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Some recent applications of Fischer carbenemetal complexes in organic synthesis
Journal of Organometallic Chemistry, 2005
{[2-(Dialkylamino)ethenyl]ethoxycarbene}chromium complexes 4 have been made available from lithiated terminal alkynes, hexacarbonylchromium, triethyloxonium tetrafluoroborate and secondary amines in a one-pot operation, in good to excellent yields. Reactions of these complexes with alkynes afford 5-dialkylamino-3-ethoxycyclopentadienes 8 with excellent chemoselectivity. From cyclopentadienes of type 8, angular and linear triquinanes, di-and triannelated benzene derivatives 24/25, steroid-like skeletons 30/31, and hexacycles 32/33 can be obtained with great facility. In addition, otherwise not easily accessible cyclopenta[b]pyrans 42/43 and novel spiro[4.4]nonatrienes 52/53 can be prepared in single operational steps from complexes 4 and terminal alkynes via [3 + 2 + 2 + 1] and [3 + 2 + 2 + 2] cocyclizations incorporating two and three alkyne units, respectively. Upon heating simple Fischer carbene complexes of type 2 with methylenecyclopropanes 64, cyclopentenones 65 are formed by formal [4 + 1] cycloadditions. New carbenemetal complexes which have different chemical reactivities can be formed in situ by transmetallation from the corresponding carbenechromium complexes. Various cyclopentenone, cyclopentene and cycloheptanone derivatives are easily accessible from these new carbenemetal (nickel and rhodium) complexes and an alkyne or an allene.
Journal of the American Chemical Society, 1993
The reactions of l-(4-hexynyl)methoxymethylenepentacarbonyl complexes 11 of the group 6 metals with alkynes lead to phenol and cyclopentenedione products, both of which are the result of cyclization with one molecule of the external alkyne and the internal alkyne in the carbene complex. All four of the possible phenol products of this reaction were independently synthesized, and the product distribution among the four isomers and the cyclopentenedione was investigated as a function of solvent, concentration, and the nature of the metal. The results of these experiments suggest that the phenol 13 arises from a vinyl carbene complexed intermediate and that the phenol 16 and cyclopentenedione 12 arise from a vinyl ketene complexed intermediate. This was confirmed by a series of methanol trapping experiments and by the isolation, characterization, and study of the chemistry of the proposed vinyl ketene complex.
Organometallics, 2009
A broad range of substituted 2-cyclopentenone derivatives are prepared by a multicomponent sequential reaction of chromium alkoxy alkynyl carbene complexes with strained bicyclic olefins. An unprecedented behavior of the carbene complexes, which react through the carbene carbon and both acetylenic carbons, in a [2+2+1]/[2+1] cascade sequence, allows the synthesis of multicomponent products, which (a) incorporate two units of the same strained bicyclic olefin, (b) incorporate two different olefins, and/or (c) involve intramolecular [2+1] reactions. Evidence of the formation of 2-cyclopentenone-derived Fischer carbene complexes as reaction intermediates is provided, as they are trapped with different types of olefins or undergo alkyne insertion. § Dedicated to Prof. J. Barluenga on the occasion of his 69th birthday.
European Journal of Organic Chemistry, 2016
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2-Methyl-I ,3-dimorpholino-l,3butadiene 1 reacted with a,a-unsaturated Fischer carbene complexes to give a wide range of different products depending on the substitution pattern. Thus, sevenmembcred rings (4, 5 and 6) could be obtained from chromium complexes 2 with aromatic or vinylic groups at the /I position. Similar results were observed when a-methyl-substituted carbene complex 7 a was used. Six-membered carbocycles (derivatives of cycloadducts 12 and 13) were isolated after reaction with both chromium and tungsten complexes bear-ing one or two alkyl groups at the /3 position (10 and 11). Moreover, cyclopentenones 20 were the main products when the starting carbene complexes were alkylsubstituted at both CI and /3 positions (19a, b) or when aromatic (19c,d) instead of vinylic complexes were used. A bicy-Keywords C-H activationcarbene complexes -
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