Reactions with lithiodithiane

Acylation with Lithiodithianes 2.4.9J Miscellaneous Reactions of Dithioacetals... 

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. ... 

Lithiodithiane is aminated by reaction with a vinyl azide, as shown in equation (38). ... 

Recently, Jones and Grayshan have reported the reaction of lithiodithiane derivatives with steroidal epoxides to effect preparation of modified steroids. Treatment of 2 ,3a-oxiranyl-5a-cholestane (46) with 2-lithio-l,3-dithiane, followed by desulphurization, yielded the 2j8-methyl-3a-cholestanol 47 (equation 48). Conversely, reaction with the epimeric epoxide 48 furnished 3a-methyl-5a-cholcstan-2j8-ol (49) (equation 49) . 

Acylating agents that have been employed are carbon dioxide, alkyl chloroformates, alkyl formates, add chlorides, esters, benzonitrile and dimethylformamide the expected acylation products from reaction with the above reagents were formed in each case. However, the N,N-dimethyl-amide derivatives of higher carboxylic acids did not yield acylated product as in the case of dimethylformamide . When R = H (equation 63), it was necessary to employ two equivalents of the lithiodithiane due to product enolate formation. 

Other reactions of electron-poor aza-heterocycles that are suspected to involve a SET mechanism include 1-lithiodithiane with pyridine (73CL1307) and 1,8-naphthyridine (78ZC382), and LDA with pyridine (82JOC599). 

The reaction of 6-deoxy-6-iodo-l,2 3,4-di-0-isopropylidene-a-D-galactopyranose with 2-lithiodithiane yields an unsaturated open chain heptose derivative (equation 36). "... 

Reaction of 2-lithiodithiane and 1,1-diethoxy-2,3-epoxypropane (4) gave the expected alcohol, which was acetylated to give (5). Hydrolysis by the new procedure gave 3-acetoxy-4,4-diethoxybutanal (6). Dehydroacetoxylation was then effected with DBU (1,5-diazabicyclo[5.4.0]undec-5-ene, 2, 101). 

Three total syntheses of racemic N-methylmaysenine (133b) have been described. The synthesis by Corey et al. [223] is based on the following key steps the formation of the C9-C10 bond by reaction of the corresponding 2-lithiodithiane with a dienal bearing the benzene nucleus (separation of diastereoisomers is required). Then, a dienoic acid was formed in order to carry out the lactamization of the resulting amino acid, which finally was submitted to carbamoylation and dithiane cleavage (Scheme 61). 

The reaction of 2-cyclohexenone with 2-lithiodithiane occurs in a 1,2-fashion to give die unsaturated hydroxy derivative, which, after rearrangement followed by deprotection, gives 3-hydroxy-l-cyclohex-enecarbaldehyde. 

Acylation of 2-lithio-l,3-dithiane derivatives occurs in satisfactory yields only when a dilute solution of the dithiane derivative is added at —78°C to a solution containing a 20-100-fold excess of the acylating agent (equation 62). The above conditions are necessary to circumvent reaction of a molecule of the reactive lithiodithiane with a molecule of previously formed 2-acyldithiane. This method offers, by subsequent removal of the dithioketal function, a route for the preparation of 1,2-dicarbonyl compounds. 

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