Kazuhiro Maruyama

Stereo- and regiocontrol of acyclic systems via the lewis acid mediated reaction of allylic stannanes with aldehydes

Abstract The reaction of crotyltrialkylstannanes (1) with aldehydes in the presence of BF3,OEt2, produces the corresponding erythro homoallyl alcohols (2) predominantly regardless of the geometry of the double bond. Further, the Lewis acid mediated reaction exhibits the enhanced Cram selectivity in comparison with other allylic organometallic reactions which proceed in the absence of Lewis acids. Use of AlCl3-i-PrOH as the Lewis acid entirely changes the reaction course; the linear adduct (12) is produced rather than the branched adduct (13). The reaction of 1-BF3,OEt2 system is applied to the short and stereoselective synthesis of the (±) Prelog-Djerassi lactonic acid (16) and (-) verrucarinolactone (19).

Zirconium enolate as a new erythro-selective aldol condensation reagent

Abstract Zirconium enolates, prepard from lithium enolates and bis(cyclopentadienyl)zirconium dichloride, undergo a facile aldol condensation with aldehydes to give predominantly the erythro product regardless of the geometry of the starting enolates.

A chemical approach towards the photosynthetic reaction center

Pyromellitimide(Im)-linked porphyrin arrays were prepared and their intramolecular electron-transfer reactions were studied by picosecond time-resolved transient absorption spectroscopy. In pyromellitimide-linked zinc porphyrin (MIm), the rates of the photoinduced charge separation (CS) and charge recombination (CR) of the product ion pair (IP) states, kcs and ~ C R , were precisely determined by tracing a characteristic sharp absorption band around 715 nm due to (1m)-. kcs is essentially solvent polarity independent, while kCR increases with solvent polarity. In 1,2-phenylene-bridged zinc diporphyrin-zinc porphyrin-pyromellitimide (D-M-Im) triads, 1(M)* is competitively quenched by D through energy transfer to give l(D)*-M-Im and by Im through CS to give D-(M)+(Im)-. Secondary IP states @)+-M-(Im)are formed via hole transfer from (M)+ to D. Sequential electron-transfer reactions that are the same type of the reaction mode of the reaction center are realized in zinc porphyrin-pyromellitimide-quinone (M-Im-Q) mads; l(M)*-Im-Q -> (M)+-(1m)--Q -> (M)+-Im-(Q)-. Finally, a more long-lived IP state is generated from D-M-Im-Q tetrads.

Porphyrin synthesis from nitrocompounds

Abstract A new porphyrin synthesis starting from nitroalkenes or their equivalents is described. For example, octaethylporphyrin, coproporphyrin, porphyrin-1,2,3,4,5,6,7,8 octapropionic acid, and 2,7,12,17 tetraarylporphyrin are prepared in good yield from readily available materials such as 1-nitropropane, nitroethane, nitromethane, and aldehydes.

Singlet excitation energy transfer in conformationally restricted zinc-free-base hybrid diporphyrins

Abstract A series of conformationally restricted zinc-free-base hybrid diporphyrins has been synthesized. Efficient intramolecular singlet-singlet energy transfer from the zinc prophyrin to the free-base porphyrin in these molecules has been studied by picosecond time-resolved fluorescence spectroscopy. The dipole-dipole Forster mechanism is proposed to be dominant in the energy transfer process on the basis of the geometry dependence of its rate. However, for shorter separations, the Dexter exchange mechanism may open an additional channel for the energy transfer.

A chemical approach toward photosynthetic reaction center

A series of conformationally restricted dimeric por- phyrins bridged by aromatic spacers has been synthesized. Soret bands of their bis-zinc complexes are split due to the exciton coupling, depending upon the geometrical relationship of the two porphyrin rings. With these dimeric porphyrins, the geometry-dependence of the intramolecular singlet excita- tion energy transfer (EN) in the zinc-free base diporphyrin system and the intramolecular electron transfer (ET) in the zinc-ferric hybrid diporphyrin system were studied by the pico-second time-resolved fluorescence spectroscopy and pico- second time-resolved transient absorption spectroscopy. It has been shown that the former process proceeds via Forster mechanism. In the latter system, both rates of the forward and backward ET were determined. The rates of the forward ET decreased upon the increase of the center-to-center distance of the two porphyrins, while the rates of the backward ET were nearly constant through the series in the range of 8-22 A of the center-to-center distance. An improved procedure has been developed for the synthesis of conformationally restricted trimeric and pentameric porphyrins as well as quinone-linked porphyrin aggregates, which will be very useful in studying the sequential and long-distance EN and ET processes.

The influence of (organo)metallics “metal-tuning” on stereo- and regio-chemical convergence in reactions of allylic carbanions with aldehydes

Abstract Although the reaction of heterosubstituted allylic carbanions ( 2 ) with aldehydes generally produces a mixture of the γ- and α-adducts ( 4 and 3 ), syn - 3 and anti - 3 can be prepared either exclusively or predominantly by the proper choice of the organometallic compound added.

Water-Soluble Porphyrins with Four Sugar Molecules

Abstract Porphyrins substituted with four sugar moieties are prepared, which are freely soluble in water and show the efficient photosensitizing activity.

Allylic organometallic way to control acyclic stereochemistry and its application to the synthesis of carbohydrates

Abstract The Cram/anti-Cram selectivity in the reactions of allylmetals with aldehydes and the erythro/threo selectivity in the reactions of substituted allylic organometallic compounds with other aldehydes can be controlled by the metal (M). Based on both selectivities, we can predict the diastereofacial selectivity of more complex systems. Finally, 1-O-methyl-2,6-dideoxyhexose and 1-O,3-O-dimethyl-4,6-dideoxyhexose are prepared.

Crotylzirconium derivatives as a new reagent for the threo selective synthesis of β-methylhomoallyl alcohols

Crotylzirconium derivatives, prepared from the reaction of crotylmagnesium chloride or crotyllithium with bis (cyclopentadienyl) zirconium dichloride, undergo a rapid reaction with aldehydes to afford the threo product predominantly. The ratio of Cram/anti-Cram product via this reagent is ca. 7525 ~ 6040.