Synthesis of Pentalene Systems Employing a Sequence of Pauson—Khand Reaction, Michael Reaction, and Desilylation.

Becheanu, Armand; Bell, Thomas W.; Laschat, Sabine; Baro, Angelika; Frey, Wolfgang; Steinke, Nelli; Fischer, Peter

doi:10.1002/chin.200640058

ChemInform

2006

DOI: 10.1002/chin.200640058

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Synthesis of Pentalene Systems Employing a Sequence of Pauson—Khand Reaction, Michael Reaction, and Desilylation.

Armand Becheanu

Thomas W. Bell

Sabine Laschat

et al.

Abstract: Cyclopentane derivativesCyclopentane derivatives Q 0030 Synthesis of Pentalene Systems Employing a Sequence of Pauson-Khand Reaction, Michael Reaction, and Desilylation. -The reaction sequence is applied to norbornene, norbornadiene and pentadiene. The resulting products are further desilylated [cf. (V)] or alkylated followed by desilylation. -(BECHEANU, A.; BELL, T.; LASCHAT, S.; BARO, A.; FREY, W.; STEINKE, N.; FISCHER, P.; Z. Naturforsch., B: Chem. Sci. 61 (2006) 5, 589-596; Inst. Org. Chem., Univ. Stuttgar… Show more

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“…One reason for the paucity of dicobalt-promoted [4 + 2] cycloaddition examples is the high propensity for PKR to occur. {Co 2 (CO) 6 }–alkyne complexes are known to undergo facile intermolecular PKR with dienes. , Moreover, acyclic dienyne dicobalt hexacarbonyl complexes were shown to prefer PKR over dicobalt-promoted intramolecular [4 + 2] cycloadditions . In our studies, dicobalt promoted transannular [4 + 2] cycloaddition reactions showed impressive selectivity, and no transannular PKR products 28 , 29 , or 30 were detected (Scheme ).…”

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Transannular [4 + 2] Cycloaddition Reactions of Cobalt-Complexed Macrocyclic Dienynes

Karabıyıkoğlu

Merlic

2015

Org. Lett.

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The first transannular [4 + 2] cycloaddition reactions of macrocyclic dicobalt hexacarbonyl−dienyne complexes were demonstrated. Complexes were conveniently prepared through palladium(II)-catalyzed intramolecular oxidative cyclization of bis(vinylboronate esters) followed by complexation with dicobalt octacarbonyl. Transannular [4 + 2] cycloaddition reactions of the complexes occurred at lower temperatures and shorter times than transannular Diels−Alder reactions of metal-free dienynes. Intermolecular control reactions confirmed the effect of cobalt complexation on [4 + 2] cycloaddition reactions of unactivated alkynes and dienes.T he transannular Diels−Alder (TADA) reaction is a potent synthetic tool for building complex organic scaffolds. 1TADA reactions are exploited in total syntheses due to their versatility, atom economy, and unique stereoselectivity.2 Studies on spinosyn A biosynthesis led to the discovery of the first pure Diels−Alderase enzyme that, in fact, catalyzes a transannular Diels−Alder transformation.3 Although TADA reactions have been widely investigated, utilization of transition metals to promote or catalyze such transformations remains poorly established. 4Cobalt−alkyne complexes are versatile species with myriad applications in synthetic chemistry. In addition to operating as protected alkynes 5 and stabilized propargyl cations, 6 dicobalt hexacarbonyl−alkyne complexes participate in several important cycloaddition reactions. 7 In particular, the [2 + 2 + 1] cycloaddition known as the Pauson−Khand reaction (PKR) is the most frequently studied. 8 However, studies on other cycloaddition reactions of alkyne−{Co 2 (CO) 6 } complexes, especially the [4 + 2] reaction, are scarce. The only reported examples of [4 + 2] cycloaddition reactions with alkyne− {Co 2 (CO) 6 } complexes are (1) intermolecular tandem Diels− Alder/Pauson−Khand reactions of a few terminal alkyne complexes with 1,3-cyclohexadiene 9 and (2) intermolecular Diels−Alder reactions with complexes of otherwise inaccessible strained and reactive cyclic alkynes.10 Despite this limited precedence, we postulated that [4 + 2] cycloaddition reactions of dicobalt complexes would make structures unattainable via metal-free Diels−Alder reactions accessible and that cobaltpromoted TADA reactions would present a unique entry to both organocobalt and macrocycle chemistry. Herein, we demonstrate the first transannular [4 + 2] cycloadditions of macrocyclic dienyne−{Co 2 (CO) 6 } complexes and the advantages over metal-free TADA reactions.We reported palladium(II)-catalyzed oxidative coupling of bis(vinylboronate esters) as a mild and facile entry to macrocyclic trienes and dienynes.11 This approach efficiently provided strained cyclic substrates, some of which, such as 2, readily underwent proximity-induced 12 TADA reactions at room temperature (Scheme 1). 13To explore TADA reactivity of 14-membered alkynes, we needed to synthesize dienyne 11 (Scheme 2). Trials to prepare triyne 9 via classical S N 2 reactions with various nucleophi...

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confidence: 52%

Transannular [4 + 2] Cycloaddition Reactions of Cobalt-Complexed Macrocyclic Dienynes

Karabıyıkoğlu

Merlic

2015

Org. Lett.

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Synthesis of Pentalene Systems Employing a Sequence of Pauson—Khand Reaction, Michael Reaction, and Desilylation.

Cited by 1 publication

References 1 publication

Transannular [4 + 2] Cycloaddition Reactions of Cobalt-Complexed Macrocyclic Dienynes

Transannular [4 + 2] Cycloaddition Reactions of Cobalt-Complexed Macrocyclic Dienynes

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