Intramolecular competitive addition of vinyl radicals to keto and alkenyl groups in Wieland–Miescher ketones—synthesis of carbocycles and propellanes

Rajamannar, T.; Balasubramanian, K. K.

doi:10.1039/c39940000025

Cited by 12 publications

(4 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…While radical cyclization onto a C=O π‐bond is facile, rate studies have shown that ring closure of radicals onto carbonyl groups is slower than ring opening of the alkoxy radical counterparts, thus rendering carbonyl groups generally unfavorable as radical acceptors. This unfavorability is reflected by the limited use of radical cyclizations, with ketones as radical acceptors, to access cycloalkanols, although in isolated examples haloalkanes, a vinylbromide, alkynes, and epoxides have been used as proradicals.…”

Section: Methodsmentioning

confidence: 99%

Radical Cyclization of Alkene‐Tethered Ketones Initiated by Hydrogen‐Atom Transfer

et al. 2017

View full text Add to dashboard Cite

An unprecedented C-C coupling reaction between alkenes and ketones by hydrogen-atom transfer, using Fe(acac) and PhSiH in EtOH, is described. This mild protocol features high site selectivity and allows the construction of sterically congested structures containing tertiary alcohols and quaternary centers. The overall process introduces a novel strategic bond disconnection for ring-closing reactions.

show abstract

Section: Methodsmentioning

confidence: 99%

Radical Cyclization of Alkene‐Tethered Ketones Initiated by Hydrogen‐Atom Transfer

et al. 2017

View full text Add to dashboard Cite

show abstract

“…Frequently, the reactions succeeded with model compounds but failed when applied to 6. Several traditional bases were examined, including KOtBu/ tBuOH, 10 Triton B/MeOH, 11 NaOEt/EtOH, and NaH/THF, but without success. Ultimately, the use of a mixture of triethylamine and KOH in ethyl acetate 12 was found to give reasonable amounts of the desired Michael adduct.…”

Section: Resultsmentioning

confidence: 99%

The Supertristeroids: Large, Chiral, Molecular Bowls Prepared by Trimerization of Pentacyclic Steroidal Ketones

Song

Pascal

2007

J. Org. Chem.

View full text Add to dashboard Cite

Robinson annulation of coprostanone (1) at the 2,3- and 3,4-positions gave two pentacyclic enones (7 and 10) that contain A/B-cis-fused ring junctions. Reduction of these enones gave the pentacyclic steroidal ketones 2 alpha,3beta- (8) and 2 alpha,3 alpha-(3'-oxocyclohexano)-5 beta-cholestane (9) and 4 alpha,3beta- (11) and 4 alpha,3 alpha-(3'-oxocyclohexano)-5 beta-cholestane (12). The structures of compounds 8, 9, and 11 were unambiguously established by X-ray analysis. TiCl4-promoted trimerization of compounds 8 and 11 gave the "supertristeroids" 4 and 5, respectively: large (C93) chiral, hydrocarbon clefts with C3-symmetric pockets approximately 12 A in diameter.

show abstract

“…Similar results were also obtained in the cases of dione substrates 1e and 1f with allyl or 2-bromoallyl group, respectively (entries 5 and 6). 11 In addition, the cyano dione 1g also proved to be well effective in this reaction, and gave the highest ee value (88%, entry 7). Furthermore, the well-known substrate, 2-methyl-2-(3-oxobutyl)-1,3-cyclohexanedione (1h), was examined (entry 8), and it proceeded smoothly to afford the expected product 2h in 87% ee in 68% yield, being better than the very recent literature report (78% ee, 57% yield).…”

mentioning

confidence: 94%

Prolinamide/PPTS-Catalyzed Hajos-Parrish Annulation: Efficient Approach to the Tricyclic Core of Cylindricine-Type Alkaloids

Zhang¹,

Wang²,

Tu³

et al. 2008

Synlett

View full text Add to dashboard Cite

A series of Wieland-Miescher ketone analogues bearing highly functionalized substituents are efficiently constructed in high enantioselectivities and good yields using catalytic amounts of prolinamide and PPTS. We have successfully utilized this reaction as a key step to synthesize the tricyclic core of cylindricine type alkaloids.The quaternary 6-6-and 5-6-fused bicyclic systems are core structures incorporated in a variety of biologically significant pharmaceutical molecules and natural products, especially in alkaloids, steroids, and terpenoids, and thus frequently demonstrated as key building blocks in the total synthesis of these interesting molecules. 1 The enantioselective construction of these bicyclic systems has been attracting high attentions since Hajos and Parrish developed L-proline-catalyzed asymmetric Robinson annulation strategy to give access to chiral C8a-methyl 6-6-and 5-6-fused bicyclic species in the early 1970's. 2 From then on, various studies have been performed toward screening the structurally diverse substrates and developing new catalysts to improve the enantioselectivity and reactivity, but most of them only focused on establishing the quaternary fused bicyclic system with simple angular methyl group. 3 In connection with our recent synthetic interests in the polycycle-fused natural products, 4 we realize that the efficient asymmetric construction of the fused bicyclic systems with functionalized chains rather than the simple methyl or ethyl group will give more impact to expeditious synthesis of some natural products with the key tricycle-fused skeletons (Scheme 1), 5 as well as some important pharmaceutical intermedicates. 6 To our knowledge, however, only few examples about the enantioselective access to this kind of synthetic structures were revealed. 7 Recently, our studies on this subject have resulted in more efficient establishment of this kind of fused bicyclic ring system with higher enantioselectivity (up to 88% ee) by using simple and easily available prolinamide and pyridinium p-toluenesulfonate (PPTS) as Scheme 1 Proposed structural diversity of tricyclic systems O

show abstract

Intramolecular competitive addition of vinyl radicals to keto and alkenyl groups in Wieland–Miescher ketones—synthesis of carbocycles and propellanes

Cited by 12 publications

References 20 publications

Radical Cyclization of Alkene‐Tethered Ketones Initiated by Hydrogen‐Atom Transfer

Radical Cyclization of Alkene‐Tethered Ketones Initiated by Hydrogen‐Atom Transfer

The Supertristeroids: Large, Chiral, Molecular Bowls Prepared by Trimerization of Pentacyclic Steroidal Ketones

Prolinamide/PPTS-Catalyzed Hajos-Parrish Annulation: Efficient Approach to the Tricyclic Core of Cylindricine-Type Alkaloids

Contact Info

Product

Resources

About