Generation and Reaction of Tungsten-Containing Carbonyl Ylides:  [3 + 2]-Cycloaddition Reaction with Electron-Rich Alkenes

Abstract

Novel tungsten-containing carbonyl ylides 7, generated by the reaction of the o-alkynylphenyl carbonyl derivatives 1 with a catalytic amount of W(CO)(5)(thf), reacted with alkenes to give polycyclic compounds 5 through [3 + 2]-cycloaddition reaction followed by intramolecular C-H insertion of the produced nonstabilized carbene complex intermediates 8. In the presence of triethylsilane, these tungsten-containing carbene intermediates 8 were smoothly trapped intermolecularly by triethylsilane to give silicon-containing cycloadducts 17 with regeneration of the W(CO)(5) species. By this procedure, the scope of alkenes employable for this reaction was clarified. The presence of the tungsten-containing carbonyl ylide 7c was confirmed by direct observation of the mixture of o-ethynylphenyl ketone 1c and W(CO)(5)(thf-d(8)). Careful analysis of the intermediate by 2D NMR, along with the observation of the direct coupling with tungsten-183 employing the (13)C-labeled substrate, confirmed the structure of the ylide 7c. Examination using (E)- or (Z)- vinyl ether revealed that the [3 + 2]-cycloaddition reaction proceeded in a concerted manner and that the facial selectivity of the reaction differed considerably depending on the presence or absence of triethylsilane. These results clarified the reversible nature of this [3 + 2]-cycloaddition reaction.

Ruthenium(0)‐Catalyzed [4+2] Cycloaddition of Acetylenic Aldehydes with α‐Ketols: Convergent Construction of Angucycline Ring Systems

“…Herein, we report that zero‐valent ruthenium catalysts promote the [4+2] cycloaddition of α‐ketols with ortho ‐acetylenic benzaldehydes, and demonstrate how this transformation enables concise construction of ring systems found in type II polyketides of the angucycline class . This cycloaddition is unique among metal‐catalyzed reactions of ortho ‐acetylenic benzaldehydes (Scheme ) …”

“…[6] This cycloaddition is unique among metal-catalyzed reactions of ortho-acetylenic benzaldehydes (Scheme 1). [7][8][9][10][11][12][13][14][15][16][17] Ty pe II polyketide natural products,s uch as the tetracyclines,d aunorubicin, and doxorubicin, have found broad use in human medicine. [18] Although total synthesis potentially offers entry to otherwise inaccessible analogues,current manufacturing routes rely on fermentation or semi-synthesis, suggesting improved methods for de novo chemical synthesis are necessary.T he most common methods used for the construction of type II polyketides are stoichiometric benzannulations, [19] such as the Hauser reaction, [20] Diels-Alder benzannulations, [21] the Dçtz reaction, [22] and aryne-mediated benzannulation.…”

The synthesis of functionalized bridged polycycles via C–H bond insertion

“…Iwasawa demonstrated a similar strategy for bridged-polycycle synthesis using a tungsten catalyst ( Scheme 27 ) [ 102 – 103 ]. Again, the formation of a 1,3-dipole (see 127 ) allows for a cycloaddition, though this example is intermolecular in nature.…”

Direct nucleophilic C-1 addition of stable isochromenylium tetrafluoroborates under catalyst-free conditions: A new access to 1H-isochromenes

“…They have been known as the proposed inseparable intermediates in a number of cycloisomerization reactions of o-alkynylbenzaldehydes in the presence of metal catalyst or promoters [9][10][11][12][13][14][15][16][17][18][19][20][21] or other electrophiles [22][23][24][25][26][27], until the recent isolation and characterizations of stable isochromenylium salts were achieved by our group [28]. These air-and moisture-stable isochromenylium tetrafluoroborates could be conveniently prepared by direct treatment of the o-alkynylbenzaldehyde precursors with HBF 4 in acetic acid.…”