1.4- Dithiane-2-carboxylates

Dithiolanes and 1,3-oxathiolanes also undergo carbene insertion on treatment with methyl diazoacetate in the presence of Rh2(OAc)4, to give 1,4-dithiane-2-carboxylates and... 

The lithium enolate derived from ethyl dithiane carboxylate reacts with aldehydes to furnish /3-hydroxy-ester derivatives in good yield. The Lewis acid-promoted additions of carbonyl compounds to donor-acceptor-substituted cyclopropanes, leads initially to /3-hydroxy-esters, which undergo subsequent conversion to chlorides or dihydrofurans (Scheme 41). "... 

The Dim ester was developed for the protection of the carboxyl function during peptide synthesis. It is prepared by transesterification of amino acid methyl esters with 2-(hydroxymethyl)-l,3-dithiane and Al(/-PrO)3 (reflux, 4 h, 75°, 12 torr, 75% yield). It is removed by oxidation [H2O2, (NH4)2Mo04 pH 8, H2O, 60 min, 83% yield]. Since it must be removed by oxidation it is not compatible with.sulfur-containing amino acids such as cysteine and methionine. Its suitability for other, easily oxidized amino acids (e.g., tyrosine and tryptophan) must also be questioned. It is stable to CF3CO2H and HCl/ether. - ... 

Ethyl l,3-dithiane-2-carboxylate [20462-00-4] M 192.3, b 75-77 /0.2mm, 96 /0.4mm, dj 1.220, n 1.5379. Dissolve in CHCI3, wash with aqueous K2CO3, 2 x with H2O, dry over MgS04, filter, evaporate and distil. [Eliel and Hartman J Org Chem 37 505 I972 Seebach Synthesis 1 17 1969.]... 

Other carbanionic groups, such as acetylide ions, and ions derived from a-methylpyridines have also been used as nucleophiles. A particularly useful nucleophile is the methylsulfinyl carbanion (CH3SOCHJ), the conjugate base of DMSO, since the P-keto sulfoxide produced can easily be reduced to a methyl ketone (p. 549). The methylsulfonyl carbanion (CH3SO2CH2 ), the conjugate base of dimethyl sulfone, behaves similarly, and the product can be similarly reduced. Certain carboxylic esters, acyl halides, and DMF acylate 1,3-dithianes (see 10-10. )2008 Qxj(jatjye hydrolysis with NBS or NCS, a-keto aldehydes or a-... 

Halogenation of 106 with triphenylphosphine, iodine, and imidazole provided the iodo derivative 109. On treatment with lithium aluminum hydride, 109 was converted into two endocyclic alkenes, 110 and di-O-isopro-pylidenecyclohexanetetrol, in the ratio of 2 1. Oxidation of 110 with dimethyl sulfoxide - oxalyl chloride afforded the enone 111.1,4-Addition of ethyl 2-lithio-l,3-dithiane-2-carboxylate provided compound 112. Reduction of 112 with lithium aluminum hydride, and shortening of the side-chain, gave compound 113, which was converted into 114 by deprotection. ... 

C-Alkylation of ethyl l,3-dithiane-2-carboxylate (for preparation, see 4.1.6) under mild soliddiquid phase-transfer catalytic conditions [32, 33] provides a potentially useful route to a-ketoesters. 

Oxidation of 1,3-dithianes to 1,3-dithiane 1-oxides has been carried out by various methods using H2O2 or /-butyl hydroperoxide (TBHP) as oxidant. In the presence of chiral co-oxidants, optically active 1,3-dithiane 1-oxides have been prepared (Scheme 66). A compilation of some currently used methods is given in Table 13. The oxidation to 1,3-dithiane 1,3-dioxides was conducted similarly. Sharpless conditions were found to be highly effective with 2-alkyl- or alkylidenyl-substituted substrates. The parent 1,3-dithiane 1,3-dioxide was obtained by basic removal of a 2-carboxyl group in 83% yield and 99% ee <1998JOC7306>. 

The dibromobutene 149 could be monosubstituted using 2-lithio-l,3-dithiane as a carboxylic acid precursor, followed by substitution of the remaining bromide with sodium azide as the amine precursor (Scheme 32). The azide was reduce under Staudinger conditions and acy-lated. After separation of the EIZ isomers, further functional group transformations gave the dimethyl-substituted Gly-Gly alkene isostere 152J123 ... 

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