Santiago Franco

Synthesis of N-Benzyl Nitrones

Abstract A general procedure for the synthesis of twenty-seven chiral and achiral N-benzyl nitrones 1 is described.

4H-Pyran-4-ylidenes: Strong Proaromatic Donors for Organic Nonlinear Optical Chromophores

Merocyanines where a polyenic spacer separates a 4H-pyran-4-ylidene moiety and different strong organic acceptors have been synthesized. According to NMR studies and X-ray diffraction data, these compounds have weakly alternated structures and remarkably zwitterionic ground states, with a partial aromatic character that is compared to those of other pyran derivatives. The proaromaticity of the 4H-pyran-4-ylidene donor lies behind the cyanine-like behavior and low (positive or negative) second-order optical nonlinearities of the shorter derivatives. On the other hand, lengthening the pi-spacer gives rise to rapidly increasing mubeta(1907) values up to 17,400 x 10(-48) esu.

New D-π-A-conjugated organic sensitizers based on 4H-pyran-4-ylidene donors for highly efficient dye-sensitized solar cells.

We have synthesized a series of four new promising D-π-A conjugated organic sensitizers with a proaromatic 4H-pyran-4-ylidene as a donor, a thiophene ring in the bridge, and 2-cyanoacrilic acid as acceptor. Comparison between different donor substituents and the modification of the thiophene ring resulted in molar extinction coefficients as high as 36399 M(-1) cm(-1) at 551 nm. The photovoltaic properties of the DSSCs demonstrate power conversion efficiencies as high as 5.4%.

Iminium Salts of ω-Dithiafulvenylpolyenals : An Easy Entry to the Corresponding Aldehydes and Doubly Proaromatic Nonlinear Optic-phores

A short, high-yielding route to omega-dithiafulvenylpolyenals (1) via the corresponding iminium salts (2) and starting from trimethyl-1,3-dithiolium tetrafluoroborate is reported. The Knoevenagel reactions of either 1 or 2 with isoxazolone-containing acceptors afford merocyanines 7 and 9, in a process that is often accompanied by a vinylene-shortening side reaction. Experimental and theoretical studies reveal that compounds 7 and 9, featuring two proaromatic end groups, are strongly polarized and show good second-order nonlinear optical responses.

Stereocontrol by diethylaluminum chloride in the addition of 2-lithiofuran and N-methyl-2-lithioimidazole to α-alkoxy nitrones. Total synthesis of 5-O-carbamoylpolyoxamic acid

Abstract The addition of the title metalated heterocycles 1 to the nitrone 2 derived from D -glyceraldehyde acetonide leads to the corresponding syn-adducts as major products (ds 88–96 %) while the reaction in the presence of Et 2 AlCl leads to anti isomers (ds 79–95 %); the synthesis of 5-O-carbamoylpolyoxamic acid from 4-O-benzyl-2,3-O-isopropylidene-L-threose via the nitrone-furan adduct is described

AN IMPROVED SYNTHESIS OF KETONITRONES

Abstract A general procedure for the synthesis of ketonitrones 2 starting from the corresponding ketones is described.

Lewis acid stereocontrolled additions of a silyl ketene acetal to 2,3-di-O-isopropylidene-d-glyceraldehyde nitrones. Synthesis of l-isoxazolidinyl nucleosides

The reaction of O -methyl- O - tert -butyldimethylsilyl ketene acetal with N -benzyl and N -methyl-2,3- O -isopropylidene- d -glyceraldehyde nitrones in the presence of boron trifluoride etherate afforded the corresponding isoxazolidin-5-ones in excellent yields and anti -selectivities. The obtained compounds were used as key intermediates for the synthesis of isoxazolidinyl nucleosides of the l -series.

Diastereoselective nucleophilic addition of acetylide to N-benzyl-2, nitrone (BIGN). Stereodivergent synthesis of β-hydroxy-α-(hydroxyamino)- and β-hydroxy-α-amino acids

Abstract The stereocontrolled nucleophilic addition of lithium trimethylsilyl acetylide to the N-benzyl nitrone (BIGN) derived from 2,3-O- isopropylidene- d -glyceraldehyde , followed by oxidative cleavage of the ensuing propargyl hydroxylamines resulted in an efficient stereodivergent synthesis of fully protected epimeric N-hydroxy α-amino esters 8 and 13 as well as the corresponding α-amino esters 9 and 14.

Stereocontrolled addition of 2-lithiothiazole to the nitrone derived from d-glyceraldehyde acetonide. A revision and extension

Abstract The sense of diastereoselective addition of 2-lithiothiazole 1a to the nitrone 2 derived from d -glyceraldehyde is reversed by the use of Lewis acids (Et 2 AlCl, TiCl 4 ) as complexing agents; the configuration of the hydroxylamine adduct obtained from 1a and 2 in the absence of the above chelating agents, previously reported from these laboratories was revised.

Synthesis, Characterization, and Optical Properties of 4H-Pyran-4-ylidene Donor-Based Chromophores: The Relevance of the Location of a Thiophene Ring in the Spacer

A series of new 4H-pyran-4-ylidene donor-based chromophores with a thiophene ring in the spacer has been synthesized. The linear and nonlinear optical (NLO) properties of these compounds have been determined and compared with the results of computational calculations. The position of the thiophene ring proved essential to optimize the figure of merit μβ, with the best results obtained when the heterocyclic system was closer to the donor moiety.