Thin‐film transistors (TFTs) based on a new n‐channel organic semiconductor (DCMT; see Figure) are reported. An electron mobility as high as 0.2 cm2/V s was observed, as well as ambipolar TFT behavior. Variable temperature measurements reveal that electron conduction is activated, with a small activation energy of 35 ± 10 meV. These results demonstrate that quinoidal oligothiophenes are a promising new class of organic semiconductors for TFTs.

[reaction: see text] The enantioselective syntheses of C-6 O-TBS- and N-Cbz-protected 2-deoxy- and 2,3-dideoxysugars have been achieved in 6-8 steps from furfural. A combination of chemo-, regio-, and diastereoselective oxidation and reduction reactions produced deoxysugars with various C-6 substitution. A key development of this route was the use of o-nitrobenzenesulfonylhydrazide (NBSH) as a diimide precursor. These overall procedures allow for the synthesis of eight deoxysugars in either enantiomeric form.

[figure: see text] The Sharpless catalytic asymmetric aminohydroxylation has been applied to 2-vinylfuran, producing beta-hydroxyfurfurylamine 5a with enantioexcess of > 86% and 21% yield from furfural. The Cbz and TBS protected amino alcohol 5a was converted into both the D- and L-isomers of deoxymannojirimycin (DMJ) and deoxygulonojirimycin in five to seven steps and 48% and 66% overall yields. The key steps include the use of an aza-Achmatowicz reaction, a diastereoselective Luche reduction, diastereoselective dihydroxylation, and a tandem Cbz deprotection/reductive amination.

The enantioselective synthesis of three 6-amino-6-deoxy sugars has been achieved in six to eight steps from furfural. A sequence of diastereoselective oxidation and reduction reactions produced Cbz-protected 6-aminomannose from furfuryl alcohol 3. The incorporation of a Mitsunobu reaction into the reaction sequence allows for the selective synthesis of both N-Cbz-protected 6-aminotalose and 6-aminogulose. The overall procedure allows for the synthesis of either enantiomer of these three aminosugars. [reaction: see text]

IntroductionThe -hydroxyfurfurylamine functionality is an important synthetic building block for various biologically important molecules. 1 Such amino alcohols can be envisioned as precursors to furan-containing amino acids 2 by oxidation of the alcohol functionality. Furthermore, oxidative cleavage of the furan ring can lead to derivatives of the amino acid serine 3 (Scheme 1). 2,3 By employing the aza-Achmatowicz reaction, 1 furan 1 can be converted into various piperidines, in particular, azasugar 4. 4 Because of our interest in studying unnatural azasugars, we are interested in an efficient asymmetric synthesis of both enantiomers of 1. Previously, Ciufolini/Wong 5 and Zhou 6 have shown that furans similar to 1 can be produced via resolution strategies. A significant improvement of this work could be realized by the development of a catalytic enantioselective procedure capable of producing either enantiomer of 1. 7 Drawing from our successful experience with the Sharpless asymmetric dihydroxylation of vinylfuran and subsequent conversion to D-and L-sugars (Scheme 2), 8 we envisioned the synthesis of 1 being readily achievable via a Sharpless asymmetric aminohydroxylation (AA) of vinylfuran, in a single transformation (Scheme 3).Sharpless and co-workers first reported the oxyamination (aminohydroxylation) of olefins in 1975 and subsequently have extended the reaction into an efficient one-step catalytic enantioselective method. 9 We were particularly encouraged by the observation of the Sharpless group that the asymmetric aminohydroxylation of electron rich styrenes proceeds with excellent enantio-and regioselectivity, providing the primary alcohol as the major isomer. 10 We felt that the polarization of the vinyl group in 1 was approximated by p-benzyloxystyrene which gave high regioselection for the primary alcohol (88:12). The dihydroxylation results for vinylfuran 8 ameliorated our concerns regarding the susceptibility of the furan ring to oxidation. 11Herein we report our application of the asymmetric aminohydroxylation to vinylfurans and a study of regiocontrol. Our ultimate goal is to extend this methodology to the synthesis of azasugars and aminosugars. 12 Results and DiscussionFollowing literature procedures, our efforts to synthesize vinylfuran were met with only mediocre results. 13 Success has been achieved using the Peterson olefination reaction on furfural 8 to generate a solution of vinylfuran 5, which can be used directly in the asymmetric dihydroxylation reaction (Scheme 2). 8 Our initial effort to extend this simple procedure to the aminohydroxylation reaction of vinylfuran, was unsuccessful using Chloramine-T as the nitrene source; 9a however, simply switching to Sharpless's alternative procedure using benzylcarbamate gave higher yields of products via simple purification. The addition of a 2 M ether solution of vinylfuran to an aqueous t-BuOH solution of the sodium salt of N-chlorobenzylcarbamate, 1 mol % of OsO 4 , and 1.2 mol % of (DHQ) 2 PHAL afforded a 42% yield of a 1:2 mixture of...