87280-01-1

Triangulenes are of current interest for potential applications in molecular electronics. We describe here a three step synthesis of the 4,8,12-trihydro[3]triangulenium cation by cascade cyclization of a tetra-benzyl alcohol precursor in triflic acid solu

A three step synthesis of the 8,12-dihydro-4H-dibenzo[cd,mn]pyren-3a2-ylium cation (triangulenium cation) is effected by cascade cyclization of a tetra-benzyl alcohol precursor in triflic acid solution. This cation is easily observed by NMR and

Fluorinated alkyl groups are important motifs in bioactive compounds, positively influencing pharmacokinetics, potency and conformation. The oxidative difluorination of alkenes represents an important strategy for their preparation, yet current methods are limited in their alkene-types and tolerance of electron-rich, readily oxidized functionalities, as well as in their safety and scalability. Herein, we report a method for the difluorination of a number of unactivated alkene-types that is tolerant of electron-rich functionality, giving products that are otherwise unattainable. Key to success is the electrochemical generation of a hypervalent iodine mediator using an “ex-cell” approach, which avoids oxidative substrate decomposition. The more sustainable conditions give good to excellent yields in up to decagram scales.

Enantioselective approaches to the construction of four complex building blocks of the structurally intricate marine macrolide known as spongistatin 1 are presented. The first phase of the synthetic effort relies on a practical approach to a desymmetrized, enantiomerically pure spiroketal ring system incorporating rings A and B. Concurrently, the C17-C28 subunit, which houses one-fifth of the stereogenic centers of the target in the form of rings C and D, was assembled via a composite of stereocontrolled aldol condensations. Once arrival at the entire C1-C28 sector had been realized, routes were devised to provide two additional highly functionalized sectors consisting of C29-C44 and C38-C51. A series of subsequent transformations including cyclization of the E ring and hydroboration to afford the B-alkyl intermediate for the key Suzuki coupling to append the side chain took advantage of efficient stereocontrol. Ultimately, complete assembly and functionalization of the western EF sector of spongistatin was thwarted by an inoperative Suzuki coupling step intended to join the side chain to the C29-C44 sector, and later because of complications due to protecting groups, which precluded the complete elaboration of the late stage C29-C51 intermediate.

The electrochemical reduction of a series of 2-haloaryl ethers containing allyl and propargyl groups under CO2 allows the synthesis of benzofuranacetic acid derivatives. This novel intramolecular cyclization- carboxylation reaction is carried out in single-compartment cells and is catalyzed by [Ni(cyclam)Br2].

A practical approach to a desymmetrized, enantiomerically pure AB spiroacetal ring component of altohyrtin A and its congeners is detailed.

Non-conjugated tetraynes 1 undergo thermal intramolecular cyclization to non-benzenoid diradicals (23) followed by radical cycloaromatization at 25°C to provide 7-dehydro-5H-benzo[d]fluoreno[3,2-b]pyran monoradical (24) and alkyl radicals (25). Hydrogen abstraction of 24 gives 5H-benzo[d]fluoreno[3,2-b]pyrans (3) which are converted to 4 by reaction with 25. On the other hand, 2 gives 5H-fluorenol (5), indicating the formation of 1,2-didehydrobenzene diradical intermediates (28 and 29). These radicals are trapped as the corresponding Diels-Alder-type products by reaction with an aromatic diene, anthracene.

The rhodium(II) acetate catalyzed behavior of ο--α-diazoacetophenone was studied.The results obtained are consistent with a mechanism in which the key step involves intramolecular cyclization of the ketocarbenoid onto the oxygen atom of the side chain to give an oxonium ylide intermediate which undergoes either C-H insertion or a competitive 2,3-sigmatropic rearrangement.The reaction of 1-diazo-9-decene-2,5-dione with rhodium(II) acetate results in cyclization of the intermediate rhodium carbenoid to give a six-ring carbonyl ylide which readily undergoes intramolecular dipolar cycloaddition.This reaction does not occur when the keto group of the diazo compound has been replaced by an ester functionality.Similar results were also obtained with cis-2-benzoyl-1-(diazoacetyl)cyclopentane.

A variety of vinylic bromoalkenyl alkenyl ethers were reacted with piperidine and a palladium acetate-tri-o-tolylphosphine catalyst.Intramolecular vinylic substitution occurred in many cases.Five-membered rings formed most easily, followed by six and then