When ethyl is infinitely different from methyl: double addition of lithiated dithianes to aromatic carboxylates revisited

The Corey-Seebach Reagent in the 21st Century: A Review

The Corey-Seebach reagent plays an important role in organic synthesis because of its broad synthetic applications. The Corey-Seebach reagent is formed by the reaction of an aldehyde or a ketone with 1,3-propane-dithiol under acidic conditions, followed by deprotonation with n-butyllithium. A large variety of natural products (alkaloids, terpenoids, and polyketides) can be accessed successfully by utilizing this reagent. This review article focuses on the recent contributions (post-2006) of the Corey-Seebach reagent towards the total synthesis of natural products such as alkaloids (lycoplanine A, diterpenoid alkaloids, etc.), terpenoids (bisnorditerpene, totarol, etc.), polyketide (ambruticin J, biakamides, etc.), and heterocycles such as rodocaine and substituted pyridines, as well and their applications towards important organic synthesis.

Base Dependent Rearrangement of Dithiane and Dithiolane under Visible-light Photoredox catalysis

The rearrangement of dithiolanes and dithianes to access disulfide-linked-dithioesters under visible-light photoredox catalysis via controlled C-S bond cleavage has been disclosed. Unlike, the usual deprotection of dithioacetals to corresponding aldehydes under the oxidative conditions, we observed unique regioselective oxidative reactivity of five and six membered cyclic dithioacetals to form disulfide-linked-dithioesters by exchanging DMAP and imidazole bases. The generality of the protocol has been demonstrated by exploring a wide range of substrates. As an application, in situ generated thiyl radical has been trapped with disulfides to prepare hetero-disulfides of potential utility. The protocol proved to be practical on gram scale quantity and relied on clean energy source for the transformation. Based on the series of control experiments, cyclic voltammetry and Stern-Volmer studies the plausible mechanism has been proposed.

Pot-Economy Autooxidative Condensation of 2-Aryl-2-lithio-1,3-dithianes

The autoxidative condensation of 2-aryl-2-lithio-1,3-dithianes is here reported. Treatment of 2-aryl-1,3-dithianes with n-BuLi in the absence of any electrophile leads to condensation of three molecules of 1,3-dithianes and formation of highly functionalized α-thioether ketones orthothioesters in 51-89% yields upon air exposure. The method was further expanded to benzaldehyde dithioacetals, affording corresponding orthothioesters and α-thioether ketones in 48-97% yields. The experimental results combined with density functional theory studies support a mechanism triggered by the autoxidation of 2-aryl-2-lithio-1,3-dithianes to yield a highly reactive thioester that undergoes condensation with two other molecules of 2-aryl-2-lithio-1,3-dithiane.

Interrupted oligomerization revisited: simple and efficient one-pot multicomponent approach to versatile synthetic intermediates

A novel multicomponent reaction allowing for a one-pot formation of three carbon-carbon bonds has been developed. It is based on in situ generation and anionic dimerization of methylenedithiane and produces a versatile synthetic equivalent of 4-hydroxy-1,3-alkanediones which, among other things, offers expeditious one-pot access to 3(2H)-furanones.

Direct screening of solution phase combinatorial libraries encoded with externally sensitized photolabile tags

Solution phase combinatorial chemistry holds an enormous promise for modern drug discovery. Much needed are direct methods to assay such libraries for binding of biological targets. An approach to encoding and screening of solution phase libraries has been developed based on the conditional photorelease of externally sensitized photolabile tags. The encoding tags are released into solution only when a sought-for binding event occurs between the ligand and the receptor, outfitted with an electron-transfer sensitizer. The released tags are analyzed in solution revealing the identity of the lead ligand or narrowing the range of potential leads.