No abstract

On treating gem-difluorocyclopropylstannanes, derived from the radical hydrostannation of gem-difluorocyclopropenes, with 1.5 equiv of MeLi in THF at -78 °C for 5 min, followed by quenching the reaction with various agents, such as H2O, alcohols, carboxylic acids, and tosylamide, the corresponding β-fluoroallylic alcohols, ethers, esters, and amide were obtained with exclusive Z-selectivity in acceptable yields.

Treatment of various gem-difluorocyclopropenes with 1.2 equiv. of n-Bu3SnH in the presence of 20 mol% of Et3B at 80 °C for 4 h led to the quantitative formation of the hydrostannylated products in a highly regio- and trans-selective manner. Additionally, the prepared trans-gem-difluorocyclopropylstannanes were treated with 1.5 equiv. of MeLi in THF at -78 °C for 5 min, followed by quenching the reaction with various agents, such as H2O, alcohols, carboxylic acids, and tosylamide, to give the corresponding β-fluoroallylic alcohols, ethers, esters, and amides respectively with exclusive Z selectivity in acceptable yields.

The chemical and redox properties of benzo-dipteridine (BDP), an oxidation-active flavin mimic, were investigated. It was found that (i) BDP undergoes 2e-redox reaction under conventional conditions, (ii) pKa-values of 2e-reduced BDP (BDP,,) are 3.6 and 8.5, respectively, (iii) a mixture of BDP,, and BDP,, forms a charge-transfer complex in aqueous solution, (iv) BDP,, exhibits a remarkably high oxidation activity (ca. 1 07-fold) toward reactions involving nucleophilic attack at the C(4a) -position compared with 3,lO-dimethylisoalloxazine (DMI), and (v) the oxidation of an NADH model by BDP,, is acidcatalysed. As a new model reaction, BDP,, was found to oxidize sulphite ion via a BDP-SO,-adduct, which decomposes unimolecularly to give BDPH-and [SO,] in aqueous solution. This is the first example of an APS (adenosine 5'-phosphosulphate) reductase model.Flavin coenzymes exhibit diverse functions such as electron transfer, dehydrogenation, and activation of molecular oxygen in biological systems.2 For instance, flavoenzymes are able to oxidize various substrates such as amines, a-amino acids, ahydroxy acids, alcohols, dithiols, nitroalkanes, etc3 In model systems, however, the substrates oxidized by the conventional flavin models so far synthesized are very limited probably due to their lack of oxidizing power. Thus, for construction of artificial flavoenzymes, we thought that a first step would be exploitation of oxidation-active flavin mimics. Such flavin mimics would be quite useful not only for mechanistic studies of the oxidations mediated by flavin but also for exploitation of new model systems. From this point of view, we have continued to search for oxidation-active flavin mimics.Electron-deficient flavins such as 8-cyan0-~ and 7,8-dichloroflavins' are known to show high oxidizing activity. However, the substituent at the 6-position of the isoalloxazine ring, which is a peri-position from N(5), occasionally reduces the reactivity owing to steric hindrance6 To avoid this disadvantage, we employed the electron-withdrawing nature of ring nitrogen atom^,^ and found that 8 -~a -, ~ 6,8-diaza-,' and 6,89-triazaflavins" show remarkably high oxidizing activity. For example, the oxidation of thiols is facilitated by factors of ca. lo6 for 8azaflavin, ca. lo8 for 6,8-diazaflavin, and ca. 10" for 6,8,9-Paper 0/008861

Alcohols. -Compound (VIg) undergoes ring-opening reactions with water, alcohols, carboxylic acids and amides as nucleophiles. The use of amines or thiols as nucleophiles gives no comparable ring-opened products. -(NIHEI, T.; HOSHINO, T.; KONNO*, T.; Org. Biomol. Chem. 13 (2015) 12, 3721-3731, http://dx.doi.org/10.1039/C5OB00046G ; Dep. Chem. Mater. Technol., Kyoto Inst. Technol., Sakyo, Kyoto 606, Japan; Eng.) -M. Tismer 29-242