Semiconductor‐Catalysed Photoaddition: γ,δ‐Unsaturated Amines from Cyclopentene and Schiff Bases

Abstract

Irradiation of methanolic cadmium sulfide suspensions in the Results and DiscussionAddition of Cyclopentene: Irradiation of a methanolic CdS suspension in the presence of the Schiff bases l a -l d and an excess of cyclopentene afforded the addition products 2a-2d and the hydrodimers 3a-3c (Scheme 1). HPLC analysis indicated a quantitative transformation of 1 a into Heterogeneous Photocatalysis, XIV. -Part XIII: 2a and 3a, the ratio of 2a to 3a being 6:l. After complete disappearance of the imine component the products were isolated in yields of 50-9576 by preparative HPLC. 3d was formed in very low concentrations and no attempts were made for its isolation.The structure of the y,6-unsaturated amines was deduced from their mass spectra and one-and two-dimensional 'Hand I3C-NMR analyses. Since the addition reaction generates two chral centers, a racemic mixture of four diastereomers was obtained. The two enantiomeric pairs could be identified in the 'H'H COSY and 'H13C COSY NMR spectrum as displayed for 2a in Figure 1.The signals of the methylene protons at C-6 and C-5 appear as a multiplet at 6 = 1.65-2.20 and 2.20-2.45, respectively. The protons at C-1 and C-2 give rise to two doublets of equal intensities at 6 = 4.15 (3J = 6.5 Hz) and 4.28 (3J = 4.5 Hz) as well as to two multiplets at 6 = 3.08 and 3.16, respectively. This and the four multiplets of the olefinic protons at C-3 (6 = 5.44, 5.52) and C-4 (6 = 5.88, 5.96) clearly indicate the presence of two diastereomers. The presence of a C-C bond between C-1 and the cyclopentenyl group at the allylic carbon atom C-2 is proved by the 'H'H COSY spectrum; the proton 1-H gives rise to an intensive cross peak with 2-H which further couples with 6-H. Whereas in the case of 2a coupling of 2-H with the olefinic proton 3-H could not be detected, this coupling was observed in the COSY spectra of the other addition products. The appearance of a set of two slightly shifted cross peak patterns is further evidence for the presence of a diastereomeric mixture (Figure 1).

Visible light mediated homo- and heterocoupling of benzyl alcohols and benzyl amines on polycrystalline cadmium sulfide

“…23 The ratio between the two products depends on the initial concentration of the substrate and time of irradiation. At an initial concentration of 0.33 mol L −1 about 90% of the amine 16c is converted to imine 18c and only 10% to diamine 17c.…”

Type B Semiconductor Photocatalysis: The Synthesis of Homoallyl Amines by Cadmium Sulfide‐Catalyzed Linear Photoaddition of Olefins and Enol/allyl Ethers to N‐Phenylbenzophenone Imine

“…For the adducts 2-5,6 and 7, and 8, isolated yields were about 75, 55, and 30 %, respectively. The reaction of 2,5-dihydrofuran (2,s-DHF) was also performed by exposing the suspension to sunlight; over 4 h Abstract in German: Neue Homoallylamine werden durch 2,2,3,Cyclopenten, Figure I . UV/Vis spectra for the CdS-catalyzed photoaddition of cyclopcntene to 1.…”

Heterogeneous photocatalysts in organic synthesis

“…38 Its formation suggests a parallel one-electron reduction process from the conduction band of the excited photocatalyst to the imine affording the a-aminobenzyl radical, which couples with an allylic radical formed from the olefin via oxidative electron transfer and deprotonation.…”