2-Dimethylamino-l,3-dioxolanes

Dimethylamino-l,3-dioxolane/cat. HOAc, CH2CI2, 83% yield. 2-Di-methylamino-l,3-dioxolane protects a reactive ketone under mild conditions it reacts selectively with a C3-keto steroid in the presence of a A -3-keto steroid. C12- and C2o-keto steroids do not react. 

Alkenes from vie -diols.2 The 2-dimethylamino-l,3-dioxolanes 1, obtained by reaction of a 1,2-diol with N,N-dimethylformamide dimethyl acetal in quantitative yield, when treated with ethyldiisopropylamine (4 equiv.) and triflic anhy-... 

Eastwood, F W, Harrington, K J, Josan, J S, Pura, J L, The conversion of 2-dimethylamino-l,3-dioxolans into alkenes. Tetrahedron Lett., 11, 5223-5224, 1970. 

Dimethylamino-l,3-dioxolanes, prepared by the reaction of the diol with dimethylformamide di-methylacetal, react in situ with Mel to give quaternary ammonium salts, which typically fragment at lower temperature (110-130 C) to give the alkene, CO2 and MeaNHI. For acid sensitive compounds such as the unsaturated acetal (46 equation 9), these conditions are superior to the original Eastwood procedure. Fragmentation of the 2-dimethylamino-1,3-dioxolane can also be effected by Ac20 and in some cases this modification is preferred, since the weakly nucleophilic acetate by-product causes fewer serious side reactions than iodide. ... 

Several unsaturated aldonlc acid derivatives have been reported. The enantiomeric 2,3-dideoxy analogues (7) of ascorbic acid have been prepared from 5,6-0 -isopropylidene-L-gulono- and D-mannono-1, -lactones by formation of their 2-(dimethylamino)-l,3-dioxolane... 

A soln. of 2,4-dibromo-2-methyl-3-pentanone in dimethylformamide added drop-wise under Ng at -35° to a suspension of zinc-copper couple in dimethylformamide, and stirring continued 10 min. at the same temp. 4-ethylidene-5,5-dimethyl-2-dimethylamino-l,3-dioxolane. Y ca. 50%. F. e. s. H.M.R. Hoffmann et al., Am. Soc. 94, 3201 (1972). 

Alkylation of a-lithio-iV,/V-dimethylhydrazones with 2-(iodomethyl)-l,3-dioxolane provides masked 7-hydrazonoaldehydes. Cyclization occurs after acid-catalyzed removal of the dioxolane protecting group and the /V-unsubstituted pyrrole can be obtained by hydrogenolysis of the N,N-dimethylamino substituent (Scheme 41) (88JHC1135). 

A soln. of acetophenone dimethylhydrazone in HMPT slowly added to a stirred soln. of LiN(Pr-/)2 in THE at — 20°, after 2 h the mixture warmed to 0°, stirred for a further 2 h, cooled to —78°, 2-iodomethyl-l,3-dioxolane added slowly, after 1 h the mixture warmed slowly to room temp., and worked up after 12 h - intermediate (Y 95%), in toluene containing -TsOH refluxed for 30 h - l-dimethylamino-2-phenylpyrrole (Y 90%), suspended in 3 1 MeOH/H20, and hydrogenated with Raney nickel at room temp, under 60 p.s.i. H2 for 48 h - 2-phenylpyrrole (Y 85%). F.e.s. G. Chelucci, M. Marchetti, J. Heterocyc. Chem. 25, 1135-7 (1988). 

Alkylation Reactions. DMF dialkyl acetals undergo a variety of reactions with 1,2-diols. For example, the reaction of trans-cyclohexane-l,2-diol with DMF dimethyl acetal leads to the formation of cyclohexane epoxide (eq 2) with inversion of configuration. Similarly, wej 0-l,2-diphenyl-l,2-ethanediol gives trans-stilbene epoxide stereospecifically (eq 3). This method has also been applied in the synthesis of cholestane epoxide from vicinal diols. If the intermediate 2-dimethylamino-1,3-dioxolane is treated with Acetic Anhydride, reductive elimination to the alkene occurs with retention of stereochemistry (eq 4). " ... 

Methyl 3,5-di-0-acetyl-2-deoxy-a-D-ery /iro-pentofuranoside, D-345 Methyl 3,4-di-0-acetyl-2-deoxy-a-L-ery /iro-pentopyranoside, D-345 Methyl 3,6-di-O -benzoyl-2,4-dideoxy-D-erj zAro -hexopyranoside, D-609 Methyl 3,5-di-O -benzyl-2-deoxy-a-L-ery /ira -pentofuranoside, D-345 Methyl 3,5-di-0-benzyl-2-deoxy-p-L-er /ira-pentofuranoside, D-345 Methyl 2,3-dideoxy-p-D-g/> C ro-hexopyranosid-4-ulose, 8CI, D-602 Methyl 2,2-dimethyl-p-oxo-l,3-dioxolane-4-propanoic acid, 9CI, D-704 Methyl 3,4,6-tri-0-acetyl-2-deoxy-a-D-/vxo-hexopyranoside, D-202 Methyl 3,4,6-tri-0-acetyl-2-deoxy-p-D-araZ in -hexopyranoside, M-171 Methyl 2,3,6-trideoxy-3-dimethylamino-a-D-/jxo-hexopyranoside, D-727 Methyl 2,3,6-trideoxy-3-dimethylamino-p-D-/jxo-hexopyranoside, D-727... 

Dioxolans. Some of the most interesting work in this series has come from Hoffmann s group in London. The debromination of aa -dibromo-ketones, e.g. (202), with a zinc-copper couple in dimethylformamide or dimethylacetamide gives 2-dimethylamino-4-methylene-l, 3-dioxolans (203). These compounds can be regarded formally as 1,3-dipolar adducts of dimethyl amides with oxyallyl (204), or as 1-amino-acetals. Their great... 

Enols and Enolates.—The search for the hypothetical oxyallyl zwitterion (36) and the invocations of its intermediacy continue unabated reductive transformations of aa -dibromo-ketones, plausible precursors of the zwitterion, have been extensively studied. Reduction of such ketones with a Zn-Cu couple in DMF yields 2-dimethylamino-4-methylene-l,3-dioxolans (37), by... 

Ole/m synthesis, Eastwood ei al. have reported a new method for conversion of W -diols into alkenes. For example, rut-1,2-diphenylethane-l,2-diol (1) is heated with N,N-dimcthylformamide dimethyl acetal to give 2-dimethylamino-/rani -4.5-diphenyl-1,.3-dioxolanc (2). When this dioxolane is heated with acetic anhydride at 165-180° rruns-stilbene (3) is formed in 80% yield. Similarly, meso-l,2-diphenylethane-l,2-diol is converted into m-stilbene (75%) and a trace of truns-stilbene if the elimination... 

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