The preparation of allenes and cumulenes

Hopf, Henning

doi:10.1002/9780470771617.ch7

Cited by 21 publications

(28 citation statements)

References 31 publications

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“…Throughout the past century, developments in the synthesis of [ n ]cumulenes ( n ≥ 5) went, more or less, hand in hand with advances in acetylene chemistry achieved by the groups of Walton, Jones, , Bohlmann, , and others. , In fact, the vast majority of all syntheses of [5]-, [7]-, and [9]cumulenes are based on α,ω-oligoyne-diols or α,ω-oligoyne-halides as precursors . In the following sections, recent examples, challenges, and advancements are used to highlight synthetic efforts used to assemble series of [ n ]cumulenes ( n ≥ 5).…”

Section: Synthesis Of [N]cumulenesmentioning

confidence: 99%

Odd [n]Cumulenes (n = 3, 5, 7, 9): Synthesis, Characterization, and Reactivity

2017

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In comparison to the omnipresent two- and three-dimensional allotropes of carbon, namely, graphite and diamond (as well as recent entries graphene, carbon nanotubes, and fullerenes), a detailed understanding of the one-dimensional carbon allotrope carbyne is not well established, and even the existence of carbyne has been a matter of controversy over the past decades. Composed of sp-hybridized carbon, carbyne could potentially exist in two forms, either as a polyyne (alternating single and triple bonds, expected to show a semiconducting behavior) or as a cumulene (all carbon atoms are connected via double bonds, predicted to show metallic behavior). Although a number of publications are available on the hypothetical structure and properties of carbyne, specific knowledge about its physical and spectroscopic characteristics is still unclear. In order to predict the properties of carbyne, the synthesis and study of model compounds, namely, polyynes and cumulenes, has been a promising avenue. The synthesis of polyynes has been extensively explored in the last decades, culminating with the isolation of a polyyne with 22 acetylene units, which allows extrapolation to the properties of carbyne. Extended cumulenes, on the other hand, have remained much less well-known, and specific studies of properties versus molecular length are quite limited. A limiting factor to the study of [n]cumulenes has been their dramatically increased reactivity, especially in comparison to polyynes of comparable length. For example, most known [7]cumulenes can only be handled in solution, while the polyynes of equivalent length (i.e., a triyne with three acetylene units) are quite stable. [9]Cumulenes are the longest derivatives studied to date. In this Account, we describe our efforts to design and synthesize odd [n]cumulenes (i.e., n = 3, 5, 7, 9) that are sufficiently persistent under ambient conditions to allow in depth characterization of physical and spectral properties. This goal has been achieved through modification of the end-capping groups by increasing the steric bulk and thereby shielding the reactive cumulene framework to provide stable [7]- and [9]cumulenes. An alternative route to stabilization is accomplished via encapsulation of the cumulene skeleton in a macrocycle, that is, formation of cumulene rotaxanes. The new sterically encumbered cumulenic products are reasonably stable under normal laboratory conditions, although some readily undergo cycloaddition reactions to give interesting products. We have explored preliminary trends for the reactivity of long [n]cumulenes. Finally, trends in the series of [n]cumulene model compounds are now discernible, including a thorough consideration of bond length alternation (BLA) in long [n]cumulenes using X-ray crystallographic analyses, as well as electronic properties via UV-vis spectroscopy and cyclic voltammetry.

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Section: Synthesis Of [N]cumulenesmentioning

confidence: 99%

Odd [n]Cumulenes (n = 3, 5, 7, 9): Synthesis, Characterization, and Reactivity

2017

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“…In preparative chemistry one of the most frequently used conjugated bisallenes is the 1,1,6,6-tetramethyl derivative of 2 , 24 (Scheme 2), which was synthesized conveniently by Skattebøl and co-workers by a route that was later termed the Doering–Moore–Skattebøl synthesis of allenes (DMS-synthesis) [23], i.e., a C 4 + C 1 + C 1 -route belonging to category (i). In this synthesis the tetramethylbutadiene 22 is first dibromocyclopropanated to the tetrabromide 23 , which, on treatment with an organolithium reagent, is debrominated/rearranged to the target hydrocarbon 24 .…”

Section: Reviewmentioning

confidence: 99%

The chemistry of bisallenes

Hopf¹,

Μαρκόπουλος²

2012

Beilstein J. Org. Chem.

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SummaryThis review describes the preparation, structural properties and the use of bisallenes in organic synthesis for the first time. All classes of compounds containing at least two allene moieties are considered, starting from simple conjugated bisallenes and ending with allenes in which the two cumulenic units are connected by complex polycyclic ring systems, heteroatoms and/or heteroatom-containing tethers. Preparatively the bisallenes are especially useful in isomerization and cycloaddition reactions of all kinds leading to the respective target molecules with high atom economy and often in high yield. Bisallenes are hence substrates for generating molecular complexity in a small number of steps (high step economy).

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“…Allenes have allowed chemists to access a variety of structurally interesting and biologically active products. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The emergence of these unique compounds in organic synthesis is a direct result of the discovery and development of efficient protocols for their preparation. Allenes can be obtained through a variety of synthetic methods, however this review focuses only on new developments or those not covered in previous reviews.…”

Section: Introductionmentioning

confidence: 99%

Synthesizing Allenes Today (1982-2006)

Brummond¹,

DeForrest²

2007

Synthesis

343

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Allenes have allowed chemists to access a variety of structurally interesting and biologically active products. The emergence of these unique compounds in organic synthesis is a direct result of the discovery and development of efficient protocols for their preparation. Moreover, efficient syntheses of the allenyl functionality are important to the synthetic community and will be reported and discussed in this review.

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The preparation of allenes and cumulenes

Cited by 21 publications

References 31 publications

Odd [n]Cumulenes (n = 3, 5, 7, 9): Synthesis, Characterization, and Reactivity

Odd [n]Cumulenes (n = 3, 5, 7, 9): Synthesis, Characterization, and Reactivity

The chemistry of bisallenes

Synthesizing Allenes Today (1982-2006)

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