Danheiser reaction

Annulations Making Use ofTrialkylsilyl Allenes (Danheiser Reactions) 829... 

In summary, the Danheiser reactions are a family of [3 + 2] annulations that take place between allenylsilanes and diverse electrophiles. The products can be carbo-cycles or heterocycles. In all cases, the annulations proceed most efficiently when the allenylsilane has a non-hydrogen substituent on the carbon atom bearing the silicon. This is a consequence of the common mechanistic pathway that proceeds through a vinyl carbocation intermediate. 

Danheiser et al. [133] reported a variety of intramolecular [4 + 2]-cycloadditions of a butenyne subunit with a remote acetylene moiety by thermolysis of the substrates, with the best yields being obtained in the presence of phenolic additives. Two examples are presented in Scheme 6.49. Of particular significance with regard to synthetic utility is the observation that protic and Lewis acids were powerful promoters of these reactions. The intermediacy of 1,2,4-cyclohexatriene derivatives, as shown in Scheme 6.49, is highly likely, at least in the non-catalyzed cases. 

Scheme 6.49 Intramolecular dehydro Diels-Alder reactions of conjugated enynes with a remote acetylene subunit furnishing annulated benzene derivatives, according to Danheiser and co-workers.

This reaction has been successfully applied to cyclopentenone annelation onto cycloalkenes. By modifying Danheiser s protocol [15], alkynyl-substituted bi-cyclo[n.l.0]alkanol derivatives are prepared by the reaction of gem-lithio-bromocyclopropanes 27 with alkynylborons, as shown in Scheme 10. 

Oximes of type XON=CW2 (X = Ts, Tf, Ac W = CN, COiEt) are of interest as cycloaddition partners in [4-1-2] cycloaddition reactions of dienes For example, addition of acetoxyimino Meldrum s acid to dienes at high pressure afforded tetrahy-dropyridine derivatives. Recently, such reactions were studied in detail by Renslo and Danheiser. Thus, Diels-Alder cycloaddition of oximinotosylate 292 with a variety of 1,3-dienes afforded tetrahydropyridines 293, which can be easily transformed to... 

Danheiser et al. developed a new aromatic annotation methodology for the total s)mthesis of hyellazole (245) by irradiation of the heteroaryl a-diazo ketone 675 in the presence of 1-methoxypropyne (590). This reaction proceeds via the photochemical Wolff rearrangement of the heteroaryl a-diazo ketone 675 to generate a vinylketene, followed by a cascade of three pericyclic reactions. 

Nowick and Danheiser have employed the Horner-Emmons reaction of a-phosphon-oacyl silanes to prepare a,/l-unsaturated acyl silanes in 54-97% yields116. The a-phosphonoacetyl silane intermediate (21), prepared from a-iodoacetyl t-butyldimethylsilane through the Arbuzov reaction, undergoes enolate alkylation, for example using potassium t-butoxide and methyl iodide the alkylated products also underwent Horner-Emmons reaction (Scheme 53). 

Materials. VTMSK (III) was synthesized in a four-step reaction sequence, as reported previously (ii). The bright-yellow monomer was stored in a sealed glass ampoule over a free-radical-polymerization inhibitor at -15 °C. IPTMSK (IV) was obtained by a procedure reported by Danheiser et al. (13) and stored as just described. All the spectroscopic properties of VTMSK and IPTMSK were in agreement with the literature data (12, 13). 

R.L. Danheiser and co-workers have used the modified Danheiser benzannuiation for the synthesis of the marine carbazole alkaloid hyellazole. The required diazoketone was prepared from the A/-Boc derivative of 3-acetylindole using a diazo transfer reaction. The diazoketone was irradiated in the presence of the alkyne to afford the desired carbazole annulation product in 56% yield. Finally, in order to install the phenyl group of hyellazole at Cl, the phenolic hydroxyl group was converted to the corresponding triflate and a Stiiie cross-coupiing was performed. 

During the total synthesis of (-)-cylindrocyclophane F, A.B. Smith et al. used the Danheiser benzannuiation to construct the advanced aromatic intermediate for an olefin metathesis dimerization reaction. The starting material triisopropylsilyloxyalkyne was synthesized from the corresponding ethyl ester using the Kowalski two-step chain homologation. ... 

Research in the laboratory of R.L. Danheiser has shown that allenylsilanes can be reacted with electrophiles other than enones, such as aldehydes and A/-acyl iminium ions to generate oxygen and nitrogen heterocycles." Aldehydes can function as heteroallenophiles and the reaction of C3 substituted allenylsilane with the achiral cyclohexane carbaldehyde afforded predominantly c/s-substituted dihydrofurans. 

R.L. Danheiser and co-workers generated a key vinylketene intermediate via tandem Wolff rearrangement-ketene-alkyne cycloaddition to utilize it in a photochemical aromatic annulation reaction Danheiser benzannulation) for the total synthesis of the phenalenone diterpene salvilenone. ... 

Danheiser benzannulation Reaction of cyclobutenones with aikynes to give highly substituted benzene rings. 122... 

Related reactions Danheiser benzannulation, Dotz benzannulation reaction ... 

Kane, J. L., Shea, K. M., Crombie, A. L., Danheiser, R. L. A ring expansion-annuiation strategy for the synthesis of substituted azuienes. Preparation and Suzuki coupiing reactions of 1-azuienyi trifiates. Org. Lett. 2001,3, 1081-1084. 

Danheiser, R. L., Nishida, A., Savariar, S., Trova, M. P. Trialkylsilyloxyalkynes synthesis and aromatic annulation reactions. Tetrahedron Lett. 1988, 29, 4917-4920. 

Danheiser, R. L., Fink, D. M. The reaction of allenylsilanes with a, 3-unsaturated acylsilanes new annulation approaches to five and six-membered carbocyclic compounds. Tetrahedron Lett. 1985, 26, 2513-2516. 

Related reactiens Bergman cycloaromatization reaction, Danheiser benzannulation ... 

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