Diradical-Promoted (n + 2 − 1) Ring Expansion: An Efficient Reaction for the Synthesis of Macrocyclic Ketones

1,3-Alkyl Transposition in Allylic Alcohols Enabled by Proton-Coupled Electron Transfer

A method is described for the isomerization of acyclic allylic alcohols into β-functionalized ketones via 1,3-alkyl transposition. This reaction proceeds via light-driven proton-coupled electron transfer (PCET) activation of the O-H bond in the allylic alcohol substrate, followed by C-C β-scission of the resulting alkoxy radical. The transient alkyl radical and enone acceptor generated in the scission event subsequently recombine via radical conjugate addition to deliver β-functionalized ketone products. A variety of allylic alcohol substrates bearing alkyl and acyl migratory groups were successfully accommodated. Insights from mechanistic studies led to a modified reaction protocol that improves reaction performance for challenging substrates.

Diversity in the Syntheses of Muscone, Muscopyridine and Civetone

Syntheses of muscone, muscopyridine and civetone since 1997 have been reviewed.

A two-step synthesis of α-keto vinyl carbinols from ketones

Conjugate addition of lithium enolates onto terminal alkynyl- and allenyl-sulfoxides furnishes the corresponding allylic sulfoxides. The latter readily undergo a Mislow-Braverman-Evans rearrangement to yield the targeted α-keto vinyl carbinols. This two-step procedure does not require purification of the intermediates and constitutes the shortest approach to α-keto vinyl carbinols.

A three-carbon (n+1+2) ring expansion method for the synthesis of macrocyclic enones. Application to muscone synthesis

The three-carbon ring expansion methodology commences with the preparation of a cyclic allene (C9, C11, C13), readily available from the corresponding cycloalkene via dibromocarbene addition and subsequent treatment with methyllithium. Dichloroketene addition to the cyclic allene regioselectively provides the [2+2] cycloadduct which is reductively dechlorinated with zinc in methanol. The resulting cyclobutanone is then catalytically hydrogenated; cyclobutanone ring opening is affected with trimethylsilyl iodide; immediate dehydroiodination of the resulting beta-iodocycloalkanone with diazabicycloundecane (DBU) provides the corresponding macrocyclic enone. The 15-membered enone was converted to dl,-muscone with (CH(3))(2)CuLi.