A [3.3]Sigmatropic Rearrangement of α,β-Unsaturated Fischer Chromium Carbenes: Synthesis of Alkynol and Dienol Esters

Söderberg, Björn C.G.; O'Neil, Shannon N.; Chisnell, Angela C.; Liu, Jian

doi:10.1016/s0040-4020(00)00216-7

Cited by 6 publications

(1 citation statement)

References 43 publications

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“…Interestingly, when vinyl ether 29 was subjected to the reaction conditions, dienal (2 E ,4 E )- 30 was formed as the major isomer in 65% yield (Scheme ) . Control experiments indicated that photoactivated tungsten hexacarbonyl and DABCO are required for the rearrangement, suggesting a vinylidene intermediate . The abbreviated reaction time also indicates that the rearrangement is preferred over cyclization, thus representing a mild entry into functionalized dienal systems.…”

Section: Resultsmentioning

confidence: 99%

Photoactivated Tungsten Hexacarbonyl-Catalyzed Conversion of Alkynols to Glycals

Wipf

Graham

2003

J. Org. Chem.

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The photoactivated W(CO)(6)/DABCO/THF system has been used for the formal endo-cyclization of alkynes to pyran rings. We found that the regioselectivity of ring closure depends on the relative configuration of the 3,5-dihydroxy-1-alkynes, as well as, more decisively, on the type of O-protective group. Oxygen substitution at the propargylic carbon slows the rate of alkyne insertion and allows for dihydrofuran formation through exo-cyclization. In contrast, the use of bulky silyl ethers or carbon substituents leads to dihydropyrans through endo-cyclization. Substrates bearing leaving groups such as esters, phenols, or thiophenols at the propargylic site eliminate and thus represent a limitation to the cycloisomerization methodology. Propargyl vinyl ethers will rearrange to give dienals instead of glycals. 1,2-Wittig rearrangement products of dihydropyrans are readily prepared and converted to complex bicyclic building blocks for organic synthesis.

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Section: Resultsmentioning

confidence: 99%