No abstract

COMMUNICATIONS OR2In the series of butatrienes only a few derivatives that exhibit functionality are known. [' -41 In particular, fewer than half a dozen papers have been published on formyl/acyl-[21 and acylo x y -s u b s t i t~t e d '~,~~ butatrienes. Established methods for the synthesis of butatrienes"] do not work for acyloxy-substituted butatrienes. In contrast, a strategy to generate butatrienic carboxylates by elimination from suitable substituted allenic precursors turned out to be extremely s u c c e s s f~l .~~] '] Elimination of hydrogen bromide from the allene 5a with sodium ethanolate in ethanol gives butatriene 6 . In contrast, elimination of hydrogen bromide from the allene 5b to give butatriene 7a is accomplished by sodium bis(trimethylsilyl)amide, whereas 5 c is dehydrohalogenated to 7b by use of sodium bis(trimethylsilyl)amide in combination with silver acetate. The cumuhomologation"21 reaction of the propadienes 5 to give butatrienes 6 and 7 is impressive in its simplicity and in the high yields obtained. Expwirncntul Procedure5 : General procedurc. To a solution of bromoalkynol 2 (7.8 g, 48 mmol) in dry toluene (70 mL) w r e added orthoester 3 (144mmol) and five drops of propionic acid, and the reaction mixture was heated for 3 h at 105-11O'~C while the generated alcohol has removed continuously in a gentle flow of nitrogen. The solvent was removed under reduced pressure, the excess of orthoester subsequently distilled off at 65-70 C.'0.5 Tori-over a Vigreux column, and the residue dissolved in diethyl ether (20 mLj. The organic layer was washed with hydrochloric acid (50 mL. 5 % ) and saturated sodium bicarbonate solution (50 mL). and then dried over magnesium sulfate. The solvent was removed under reduced pressure. and the product purified by vacuum distillation. Yields: 60-85%.

Reaction of carbonyl compounds 1 with trimethylsilylacetylene 2 leads to the alkynols 3, which are excellent precursors of acceptor-substituted allenes. Compound 3 reacts with carbamoyl chloride 4, diethyl chlorophosphate 6, or hypohalite 8 to give the substituted alkynols 5, 7, 9. Reaction of 9 with sulfinyl chloride 10 leads to the sulfinic esters 11, which on heating undergo a [2,3]-sigmatropic shift to yield the halosulfonyl allenes 12. In the same manner the reaction of 7 and 9 with chlorophosphanes 13 or sulfenyl chlorides 15 gives rise to the generation of the phosphoryl allenes 14 and the haloallenyl sulfoxides 16, respectively. Alkynyl ketene acetal intermediates 18 are formed by starting from the alkynols 9 and orthoesters 17. Spontaneous [3,3]-sigmatropic rearrangement of 18 gives the haloallenyl esters 19. Reaction of alkynols 5 with sulfur dichloride leads to the alkynylsulfinyl esters 20, which on heating rearrange to the bisallenyl sulfones 21. Pyrolysis of 21 yields the thiophene 1,l-dioxides 22. Bisphosphorylbisallene 24 is synthesized from hexadiyndiol23 by reaction with chlorodiethoxyphosphite. Halophosphoryl allenes 14 react with bromine to yield the oxaphospholenes 25 by cyclization and subsequent elimination of ethanol, or oxaphospholenes 26, if no appropriate leaving group is present in the molecule. Sulfonyl-1,3-dienes 27 can be synthesized by reaction of halosulfonylallenes 12 with bromine, followed by elimination of HBr. Haloallenyl ester 19a is converted in a non-generalizable reaction with bromine into the tribromo-3,6-dihydro-2-pyranone 30.During our recent investigations of acceptor-substituted allenes we accomplished the synthesis of allene-1, l-dicar- For the synthesis of the 1-halo-1-sulfonylallenes 12 the halo alkynols 9 are treated with the sulfinyl chlorides 10 in the presence of triethylamine. The primarily formed alkynylsulfinyl esters 11 are surprisingly stable. Only by heating of 11 in toluene at 80°C is the isomerization to the allenes 12 via [2,3]-sigmatropic rearrangement[l4I achieved quantitatively. Reaction of the alkynols 7 and 9 with chlorophosphanes 13 or sulfenyl chlorides 15 in the presence of triethylamine yields directly the allenylbisphosphonic diethyl ester 14a, the 1-halo-1-phosphorylallenes 14b-m and the 1-halo-allenyl 1-sulfoxides 16, respectively. In the case of 14 and 16, the in situ generated alkynyl derivatives, corresponding to the alkynylsulfinylesters 11, cannot be isolated, but rather undergo spontaneous [2,3]-sigmatropic rearrangement to the observed products 14 and 16.

Wer hätte das gedacht? In nur vier Stufen erhält man ausgehend von kommerziell erhältlichen Alkinolen acceptorsubstituierte Butatriene 1 in guten Gesamtausbeuten. Im wichtigsten Schritt der Synthese werden Allene einfach „verlängert”︁ .

Reaction of (2-bromophenylethynyl)trimethylsilane 1 with trimethyl borate yielded the alkynearylboronic acid 2, which was coupled in situ with the bromoallenes 3 to give enyne−allenes 4. The intermediates 4 underwent a spontaneous cation-mediated C2−C7 cycloaromatization with a concomitant 1,2-shift of the trimethylsilyl group to give the naphthalene derivatives 5. Besides 5, yne−allenes 10 were isolated by chromatography of the crude reaction products. A key step in the formation of 10 is the hydrolysis of the aryl boronic acid 2, which led to phenylethynyltrimethylsilane 8. Under the reaction conditions used, the TMS group of 8 was subsequently removed to give phenylacetylene 9, which further reacted with the bromoallenes 3 to furnish the yne−allenes 10.