Versatile Syntheses of Alkynyl- and Substituted Alkynylcyclopropanes: 2-Alkoxyethynylcyclopropanes for the Anellation of Bicyclo[3.3.0]octane Fragments

Militzer, Hans‐Christian; Schömenauer, Sten; Otte, Carola; Puls, Carsten; Hain, Jürgen; Bräse, Stefan; Meijere, Armin de

doi:10.1055/s-1993-25988

Cited by 86 publications

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“…Preparation of various alkenylboronates and alkenylstannanes: In order to be able to test the possibilities of carrying out sixfold Suzuki-and Stille-type couplings with hexabromobenzene (20), a number of 2-substituted ethenylboronates 2 and 4 and trialkylethenylstannanes 19 were prepared by hydroboration and hydrostannylation, respectively, of the corresponding terminal alkynes 3.…”

Section: Resultsmentioning

confidence: 99%

“…(1'-Methylcyclopropyl)ethyne (3 d) was prepared by treatment of the lithiated species of (2'-trimethylsilylethynyl)cyclopropane (7) [20] with dimethyl sulfate followed by hydrodesilylation in 64 % overall yield. [21] Scheme 1.…”

Section: Resultsmentioning

confidence: 99%

“…E/Z-diastereomeric mixtures of 19 were used without separation, because the Stille cross-coupling always yields the thermodynamically more stable (E)-isomers. [28,29] Sixfold cross-couplings with hexabromobenzene: An initial attempt to perform a sixfold coupling of hexabromobenzene (20) with tert-butylethenylboronate 2 a, applying [PdCl 2 (PPh 3 ) 2 ] as a catalyst and sodium ethoxide in ethanol as a base, only led to partial dehalogenation of 20. This kind of reductive dehalogenation has frequently been observed in Suzuki couplings, [13a] and found to be suppressed upon use of sodium hydroxide as a base.…”

Section: Resultsmentioning

confidence: 99%

“…[33] Even under the optimized conditions, attempted analogous cross-coupling reactions of hexabromobenzene (20) with styryl-and n-nonenylboronates did not yield any of the sixfold coupling products, [29] but only octadecadiene 22 as the homocoupling product of the corresponding boronate, when dichloro[1,1-bis(diphenylphosphano)ferrocene]palladium in THF/DMF was applied. With [PdCl 2 (PPh 3 ) 2 ], only a mixture of reduction products derived from hexabromobenzene (20) was obtained. Apparently, the tert-butyl groups in 2 a are essential for the success of the sixfold coupling, and indeed catechol (alkenyl)boronates with other tert-alkyl groups gave the corresponding sixfold coupling products 1 ch reasonably well in yields ranging from 10 to 44 % ( Table 3).…”

Section: Resultsmentioning

confidence: 99%

“…[5] An elegant route to hexaalkylbenzenes is by sixfold alkylation of hexamethylbenzene activated as a cationic cyclopentadienyliron complex under basic conditions as developed by Astruc et al [6] The sixfold coupling of hexahalobenzenes with alkynes and alkenes under palladium catalysis [ Abstract: Palladium-catalyzed sixfold coupling of hexabromobenzene (20) with a variety of alkenylboronates and alkenylstannanes provided hexaalkenylbenzenes 1 in up to 73 % and 16 to 41 % yields, respectively. In some cases pentaalkenylbenzenes 21 were isolated as the main products (up to 75 %).…”

Section: Introductionmentioning

confidence: 99%

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Six‐ and Eightfold Palladium‐Catalyzed Cross‐Coupling Reactions of Hexa‐ and Octabromoarenes

Stulgies

Prinz

Magull

et al. 2004

Chemistry A European J

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Palladium-catalyzed sixfold coupling of hexabromobenzene (20) with a variety of alkenylboronates and alkenylstannanes provided hexaalkenylbenzenes 1 in up to 73 % and 16 to 41 % yields, respectively. In some cases pentaalkenylbenzenes 21 were isolated as the main products (up to 75 %). Some functionally substituted hexaalkenylbenzene derivatives containing oxygen or sulfur atoms in each of their six arms have also been prepared (16 to 24 % yield). The sixfold coupling of the less sterically encumbered 2,3,6,7,10,11-hexabromotriphenylene (24) gave the desired hexakis(3,3-dimethyl-1-butenyl)triphenylene (25) in 93 % yield. The first successful cross-coupling reaction of octabromonaphthalene (26) gave octakis-(3,3-dimethyl-1-butenyl)naphthalene (27) in 21 % yield. Crystal structure analyses disclose that, depending on the nature of the substituents, the six arms are positioned either all on the same side of the central benzene ring as in 1 a and 1 i, making them nicely cup-shaped molecules, or alternatingly above and below the central plane as in 1 h and 23. In 27, the four arms at C-1,4,6,7 are down, while the others are up, or vice versa. Upon catalytic hydrogenation, 1 a yielded 89 % of hexakis(tert-butylethyl)benzene (23). Some efficient accesses to alkynes with sterically demanding substituents are also described. Elimination of phosphoric acid from the enol phosphate derived from the corresponding methyl ketones gave 1-ethynyladamantane (3 b, 62 % yield), 1-ethynyl-1-methylcyclohexane (3 c, 85 %) and 3,3-dimethylpentyne (3 e, 65 %). 1-(Trimethylsilyl)ethynylcyclopropane (7) was used to prepare 1-ethynyl-1-methylcyclopropane (3 d) (two steps, 64 % overall yield). The functionally substituted alkynes 3 f-h were synthesized in multistep sequences starting from the propargyl chloride 11, which was prepared in high yields from the dimethylpropargyl alcohol 10 (94 %). The alkenylstannanes 19 were prepared by hydrostannation of the corresponding alkynes in moderate to high yields (42-97 %), and the alkenylboronates 2 and 4 by hydroboration with catecholborane (27-96 % yield) or pinacolborane (26-69 % yield).

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Six‐ and Eightfold Palladium‐Catalyzed Cross‐Coupling Reactions of Hexa‐ and Octabromoarenes

Stulgies

Prinz

Magull

et al. 2004

Chemistry A European J

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Highly Functionalized Bicyclo[3.2.1]octane Derivatives from Readily Available 2′-Alkoxytricyclo[3.2.1.02,7]octanes: Building Blocks for Terpenes, Part I

Meijere¹,

Hadjiarapoglou

Noltemeyer

et al. 1998

Eur. J. Org. Chem.

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2′‐Alkoxytricyclo[3.2.1.02,7]octanes 4‐R are obtained in good to excellent yields from methyl 2‐chloro‐2‐cyclopropylideneacetate (3) and the dienolates derived from the 3‐alkoxycyclohex‐2‐enones 1‐R and 2‐R, by a cascade of two consecutive Michael additions and a γ‐elimination. Compounds 4‐R are transformed to the correspondingly substituted bicyclo[3.2.1]octanecarboxylates 5 by treatment with acid. 2′‐Methoxytricyclooctanes 4a−d‐Me are readily deprotonated to give chelation‐stabilized cyclopropyllithium derivatives 6‐Me, which react with electrophiles to yield the 7′‐substituted tricyclo[3.2.1.02,7]octanes 4f−i‐Me (61−66%). By acidic workup of such reaction mixtures, or subsequent treatment of the isolated products 4f−i‐Me with acid, efficient transformation to the correspondingly substituted bicyclo[3.2.1]octanecarboxylates 5 is observed.

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Cyclopropylacetylene

2003

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Versatile Syntheses of Alkynyl- and Substituted Alkynylcyclopropanes: 2-Alkoxyethynylcyclopropanes for the Anellation of Bicyclo[3.3.0]octane Fragments

Cited by 86 publications

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Six‐ and Eightfold Palladium‐Catalyzed Cross‐Coupling Reactions of Hexa‐ and Octabromoarenes

Six‐ and Eightfold Palladium‐Catalyzed Cross‐Coupling Reactions of Hexa‐ and Octabromoarenes

Highly Functionalized Bicyclo[3.2.1]octane Derivatives from Readily Available 2′-Alkoxytricyclo[3.2.1.02,7]octanes: Building Blocks for Terpenes, Part I

Cyclopropylacetylene

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