When Ethyl Is Infinitely Different from Methyl:  Double Addition of Lithiated Dithianes to Aromatic Carboxylates Revisited

Abstract

Addition of lithiated alkyl dithianes to benzoyl chloride or methyl benzoate does not produce the expected product of double addition, alpha,alpha-bis(alkyldithianyl) benzyl alcohol, for alkyls larger than methyl. Instead, the first step intermediate, i.e. 2-benzoylated dithiane, undergoes an electron-transfer reduction by the second molecule of the dithianyl anion. This reduction is followed by the ring-opening mesolytic fragmentation of the dithiane ring in the ketyl anion radical and subsequent radical recombination yielding acetophenone-tethered thioortho esters 4, alpha-[3-(2-alkyl-1,3-dithiane-2-ylthio)propylthio]-alpha-alkyl-acetophenones. It appears that the Corey-Seebach bisaddition of lithiated dithianes to methyl benzoate is an exception rather than the rule in the alkyl dithiane series.

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

“…Weakening of the carbon–oxygen bond from F to G is visible by its length (1.23 Å in F and 1.29 Å in G ) and weaker Wiberg index in the lithium enolate product G (WI = 1.65 in F and 1.31 in G ), accompanied by strengthening of the C–C bond (1.55 Å; WI = 0.95 in F and 1.40 Å; WI = 1.47 in G ). Although we cannot rule out a radical mechanism based on our calculations (as suggested by Kutateladze 23 and considered in Supporting Information ), the low energy barrier determined for the ionic nucleophilic attack might indicate this as the main route for formation of the orthothioester product.…”

“… 20 Presence of dimers derived from single electron transfer processes have been observed in several other works, 12a , 14c , 21 especially in the presence of nitro substituted compounds. 22 The nucleophilic addition of 2-lithio-1,3-dithianes to acyl chlorides and esters reported by Kutateladze and co-workers 23 is one example from the vast array of dithiane umpolung reactivity of carbonyl compounds ( Scheme 1 ). Interestingly, when an aldehyde other than acetaldehyde is used, the reaction proceeds through addition of a second dithiane molecule through ring-opening of the first installed dithiane unit.…”

Interrupted Oligomerization Revisited: Simple and Efficient One-Pot Multicomponent Approach to Versatile Synthetic Intermediates

“…Ketones can also be used as capping electrophiles, as exemplified by acetone. However, esters and acyl chlorides undergo a more complex electron transfer initiated reaction, similar to the radical reductive ring opening described earlier for bulky dithianes …”

Base dependent 1,3-dithioacetals rearrangement over sulfoxidation under visible-light photocatalysis to access disulfide-linked-dithioesters

“…14,15 Alternatively, researchers have explored different transformations by exploring the potential utility of in-situ generated lithiatedthioacetals that is known to proceed through the cleavage of single C-S bond of thioacetals. 16,17 However, these protocols require low temperature and strong base such as n-butyl lithium. Schmink and coworkers demonstrated synthesis of dithioether via the selective cleavage of C-S bond of thioacetals in the absence of oxidizing reagent however at an elevated temperature using metal catalyst Pd(OAc)2.…”