2- Lithio-2-methyl-l ,3-dithiane

Carbon nucleophiles of type (iii) add to the arene ligand and do not rearrange examples include the very reactive anions, such as 2-lithio-2-methyl-l,3-dithiane, and the less sterically encumbered anions, such as lithio acetonitrile and /-butyl lithioacetate. In these cases, the anion adds to an unsubstituted position (mainly ortho or meta to Cl, as in 22) 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, as from (22) in Scheme 8. 

An impressive example is the reaction of 2,6-dimethyl-1-fluorobenzene-Cr(CO)3 with 2-lithio-2-methyl-l,3-dithiane at —78 °C, followed by treatment with trifluoroacetic acid at —78 °C (equation 105). Loss of HF leads to the 1,2,4 (tele)... 

A novel method for the stereospecific synthesis of 17a- and 17) - homocorticoid side-chains from 17-ketones has been developed.The 17-oxiran (520), obtainable in high yield from the 17-ketone and dimethylsulphonium methylide, reacts with 2-lithio-2-methyl-l,3-dithian to afford (521) which on further treatment gives the 17-iso- homocorticoid (522) in high overall yield. Similar reaction of the 17-epimeric oxiran, which could not be separated from (520), afforded the normal... 

Oxidation of aldehydes to esters and acids Treatment of 2-lithio-2-alkyl-l,3-dithianes (1) with methyl disulfide in THF gives the corresponding orthothioformates (2) in about 90% yield. These are converted in high yield into esters (3) when refluxed in an aqueous alcohol in the presence of mercuric chloride and mercuric oxide as catalysts. Conversion to acids is accomplished by refluxing (2) in aqueous acetone for 24 hr. with catalysis by mercuric chloride and mercuric oxide. Yields in this case are in the range 40-65 %. 

The ring opening of enantiopure IV-tosyl aziridines 215 with 2-substituted 2-lithio-l,3-dithianes takes place at the less substituted carbon atom in good yields (59-92%)321. The corresponding adducts gave /9-tosylamino carbonyl compounds after reaction with methyl iodide under acetone reflux. 

The use of 4,5-dihydro-2-lithio-5-methyl-l,3,5-dithiazine instead of 2-lithio-1,3-dithian gives better results in the chain extension of sugars, the former being more reactive and the products more readily desulphurized. ... 

Ethynyl-l,3-dithiane when treated with 1.1 equiv. of n-butyllithium then with methyl iodide af-fords- - only the y-products as a 1 1 mixture of alkyne and allene, resulting from the direct methylation of the lithioalkyne and of the "y-methylation of 2-ethynyl-2-lithio-l,3-dithiane respectively (Scheme 72,... 

The 1,2-adducts (32) of 2-litho-l,3-dithians and cyclohex-2-enone can be isomerized to the more stable 1,4-adducts (33) by conversion into the potassium alkoxides (but not the less dissociated sodium or lithium salts).Direct formation of enone 1,4-adducts occurs when HMPA-THF is used as the solvent, and enolate trapping can be effected when the initial enone 1,4-adduct is treated with methyl iodide.The allylic anion derived from (34) undergoes cr-1,4-addition to cyclohexenone in the presence of Cul (Scheme 2). In the absence of the copper salt, both y-1,4- and cr-1,4-addition occur, with the former predominating. In contrast, allylation of (34) in the presence of Cul occurs primarily at the y-position, while cr-allylation is observed otherwise.The lithio-anion of 2-(yff-styryl)-... 

Aldehydes were converted into the corresponding esters by initial dithian formation, metallation, reaction with dimethyl disulphide, and finally hydrolysis of the 2-thiomethyl-l,3-dithians so obtained with HgClj-HgO in aqueous alcohols.The yields of methyl or ethyl esters were high but attempts to prepare t-butyl esters by this route failed and produced only acids in moderate yield. Thiomethylation or deuteriation of the allylic lithio-salt (113) occurred exclusively a to sulphur. Dithianyl carbanions... 

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. ° ... 

Lithio-2-(2,2-dimethoxyethyl)-l,3 dithian, when it reacted with ketcmes and epoxides, led to intermediates which were converted in somewhat low yield into 3-furanones and dihydro-y-pyrones, respectively. " 2-Methyl-2-lithio-dithian reacted efficiently with spiro-epoxide groups at positions 3 and 17 in steroids. The products obtained in this manner were further elaborated for example, 3a-ethyl-30-hydroxy-5a-cholestane, " 3-acetonyl-A -androstane, and both isomers of 17-acetonyltestosterone " were prepared. The carbon skeleton, including the S-lactone ring, of pestalotin... 

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. 

The /-/ -bcnzcncmolybdcnum tricarbonyl complex 187 also suffered nucleophilic addition of 2-lithio-l,3-dithiane or its 2-methyl derivative at — 78 °C to give the ry -cyclohexadienyl anionic complexes 188, which were trapped with allylic bromides to yield, after CO insertion under CO pressure, trans-5,6-disubstituted 1,3-cyclohexadiene derivatives 189 (Scheme 55)253. Analogous reactions with [( 6-benzene)Cr(CO)3] give directly the corresponding cyclohexadiene in which the CO has been inserted in the allyl group. 

Reaction of lithiodithianes with acyl chlorides, esters or nitriles leads to the fOTination 1,2-dicarbonyl compounds in which one of the carbonyl groups is protected as the thioacetal. d76043j44 Optically active amino ketones of type (69) are inepared via acylation of dithiane with an oxazoline-protected (5)-serine methyl ester (Scheme 41). Optically active (5)-2-alkoxy-l-(l,3-dithian-2-yl)-l-propanones were prepaid by the reaction of the corresponding methyl (5)-lactate with 2-lithio-l,3-enantioselective synthesis of (-)-trachelanthic acid. Enantioselective synthesis of L-glyceraldehyde involves the acylation of a dithiane glycolic acid derivative followed by bikers yeast mediated reduction. ... 

The methylations of l,3-dilithio-5,7-dimethyl-2,4,6,8-adamantane and of 1,3,5,7-tetrathiacyclooc-tane tetraanion- are of theoretical value only. 1,3,5-Trithiane and both mono- and 2,4,6-trialkyl-substituted derivatives have been metallated - with n-butyllithium and alkylated - with reactive alkylating agents such as primary alkyl iodides or bromides and benzyl bromide (Scheme 73, entries a and b). The metallation of monoalkylated trithianes occurs at one of the two unsubstituted sites and leads eventually to the product having both substituents in the equatorial position. - Thus the high equatorial preference for lithium in 2-lithio-l,3-dithiane is also present in 2-lithio-2-methyl-l,3,5-trithiane. Mer-... 

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