Radical fragmentation of omega-bromoalkyl cyclobutanones. A modular approach to eight-membered carbocycles

Stereospecific Synthesis of Enantioenriched Alkylidenecyclobutanones via Formal Vinylidene Insertion into Cyclopropanone Equivalents

1-Sulfonylcyclopropanols are employed here as efficient cyclopropanone equivalents in a formal vinylidene insertion process, providing the first general synthetic route to enantioenriched alkylidenecyclobutanones. The addition of an alkenyl-Grignard reagent leads to an alkenylcyclopropanol capable of electrophilic activation by N-bromosuccinimide, triggering a regio- and stereospecific 1,2-migration and affording alkylidenecyclobutanones after elimination. Activation of the intermediate with other electrophiles such as HCl or mCPBA leads to the formation of various chiral cyclobutanones and γ-lactones via alternative pathways.

Organic dye-catalyzed radical ring expansion reaction

Herein, we reported an attractive method for synthesizing medium-sized rings that are catalyzed by erythrosine B under fluorescent light irradiation. This synthetic approach featured mild conditions, a facile procedure, a broad substrate scope, and moderate-to-good yields.

Herein, we reported an attractive method for synthesizing medium-sized rings that are catalyzed by erythrosine B under fluorescent light irradiation.

A tandem Prins/Schmidt reaction approach to marine alkaloids: formal and total syntheses of lepadiformines A and C

The tricyclic core of the cylindricine or lepadiformine families of alkaloid natural products was assembled via a Prins addition/intramolecular Schmidt rearrangement under Lewis acid conditions. Both single-pot and two-stage variations of this process were examined, with particular attention to the stereochemical outcome of the processes. This technology has been applied to a formal total synthesis of lepadiformine A and a total synthesis of lepadiformine C.

Conjugated imines and iminium salts as versatile acceptors of nucleophiles

Growing interests in nitrogen-containing molecules involving bioactive and functional materials have stimulated the recent development of synthetic methodologies where nucleophilic addition reactions to imino carbons are utilized in crucial steps. This article summarizes double nucleophilic addition reactions with alpha,beta-unsaturated aldimines, addition reactions using alkynyl imines, "umpoled" reactions of alpha-imino esters, and the use of iminium salts as reactive electrophiles.

Acid- and Pd(0)-Catalyzed Ring Opening of 1-(1-Cycloalkenyl)cyclopropyl Sulfonates

We report herein facile acid-catalyzed isomerization of 1-(1'-cycloalkenyl)cyclopropyl sulfonates under mild conditions. The remarkable ease of ring opening is attributed to the presence of a 1'-alkyl substituent. Also included is a palladium-catalyzed ring opening reaction of 1-(1'-cycloalkenyl)cyclopropyl tosylates for convenient preparation of substituted 1,3-dienylamines, which complements previously reported nucleophilic substitution reactions of (1-vinyl)cyclopropyl tosylates.

Diastereoselective Prins-type reaction of cycloalkenylcyclopropanol silyl ethers and alpha,beta-unsaturated aldehyde acetals

Electrophilic addition of 1-(1-cyclohexenyl)-1-cyclopropanol trimethylsilyl ether to alpha,beta-unsaturated aldehyde acetals under Lewis acidic conditions proceeds with good to excellent diastereoselectivity to afford spirocyclobutanones containing three contiguous stereocenters. A convenient entry to enantioselective syntheses is available by use of a nonracemic C2-symmetric acetal. Elaboration of the resulting adducts provides ready access to medium-sized carbocycles.

Formation of five-membered carbocycles by intramolecular palladium-catalyzed ring opening of tert-cyclobutanols

We report herein stereoselective formation of a functionalized five-membered carbocycle bearing a quaternary center by intramolecular palladium-catalyzed ring-opening of o-bromophenyl-tethered tert-cyclobutanols.

Cleavage of Activated Cyclic Amines: Unprecedented Approach toward 2-Substituted Cyclobutanones

We report, for the first time, ring opening of activated four- to six-membered cyclic amines followed by an intramolecular expansion of cyclopropanol to cyclobutanone via carbocation intermediate. In the case of a N-tosylaziridine ester, a cyclobutanol was formed in a stereospecific manner during the Kulinkovich reaction step.