2-Lithio-2-phenyl-l ,3-dithiane

Lithio-2-phenyl-l,3-dithiane (17) has been employed in a new umpolung asymmetric addition of A-sulfinylimines, using a Lewis acid catalyst (Et2AlCl). The high (g) des obtained open up a new route to enantiopure a-amino ketones.70... 

Several compounds have been prepared by nucleophilic substitution of chlorine in 2-chloro-l,3-dithian with Grignard reagent (RMgBr), malonic esters, and phenols.A mechanism for the de-ethoxycarbonylation of the 2-(l,3-dithianyl)malonates by sodium chloride or sodium ethoxide has been studied. 2-Chlorotetrahydrofuran reacts with nucleophiles such as 2-lithio-2-phenyl-l,3-dithian (326) by three simultaneous mechanisms i.e. substitution, proton abstraction, and electron transfer) to give the products (327)—(330) (Scheme 12)/° When a dithian (331 R = H or COiMe) was treated with a sulphonyl chloride in pyridine, ring-expansion to the 5//-l,4-dithiepin (332) occurred instead of the expected formation of a sulphonate. ... 

Treatment of 2-lithio-2-phenyl-l,3-dithiane with 2-bromopyridine gave the substituted pyridine 44 in 50% yield . However, reaction with 2,4-dinitrobromobenzene gave none of the substitution product, but rather compound 45 resulting from oxidative dimerization of the dithiane... 

Carbon nucleophiles of type (c) add to the arene ligand and do not rearrange except in special cases examples include very reactive anions such as 2-lithio-2-methyl-l,3-dithiane and phenyl lithium. In these cases, the anion adds to an unsubstituted position (mainly ortho or meta to Cl, (e.g., 19a,b, Scheme 3) and does not rearrange. Then iodine quenching, even after a long period at 25 °C, gives almost exclusively the products from formal substitution for hydrogen. 

Lithio-2-(l-methyl-2-alkenyl)-l,3-dithianes showed 1,3-iyn selectivity on addition to aldehydes (equation 34). The presence of a bulky substituent on the dehyde gave increased syn selectivity in the following order alkyl > phenyl > 1-silylalkenyl > alkenyl > aUcynyl. Activation of an aldehyde by BFs EtaO reduced the ratio. ° ... 

Reactions of 2-lithio-l,3-dithiane (161) with nitroarenes gave 1,4- and 1,6-addition products whereas 2-methyl and 2-phenyl-l,3-dithiane derivatives provide only 1,6-addition products. These conjugate-addition products are transformed into the respective nitroaromatic compounds by in situ oxidation with oxygen or DDQ. In the case of 4-chloronitrobenzene, the 1,4-addition product with respect to the nitro group was mainly obtained242. A SET mechanism was proposed242, as in the case of alkyl iodides243. 

Addition of lithium salts enhances the stereoselectivity of the attack by MeLi on 4-t-butylcyclohexanone (87—94% equatorial attack)." Other work has shown that free Li ions are crucial for the addition of alkyl-lithium to a carbonyl function to take place, and that the cation plays a role in determining the preferred direction of the addition." The reaction of 2-phenyl-2-lithio-l,3-dithian and 4-t-butylcyclohexanone in tetrahedrofuran is thermodynamically controlled, giving the axial alcohol only. ... 

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