Preparation of Cyclobutene Acetals and Tricyclic Oxetanes through Photochemical Tandem and Cascade Reactions

Abstract

We describe a photochemical reaction using two starting materials, a cyclopent-2-enone and an alkene, which are transformed in a controlled manner via the initial [2+2]-photocycloaddition adducts into cyclobutene aldehydes (conveniently trapped as stable acetals) or unprecedented angular tricyclic 4:4:4 oxetane-containing skeletons. These compounds are formed through tandem or triple cascade photochemical reaction processes, respectively. Small libraries of each compound class were prepared, thus suggesting that this photochemistry approach opens new opportunities for synthesis design and for widening molecular diversity.

Controlling Chain Coupling and Single‐Chain Ligation by Two Colours of Visible Light

“…While classical thermally driven organic chemistry holds the potential to create such systems, it would require the use of additional reagents and chemical modification of the reactive groups, for example, protecting groups, in order to control the reaction of the parent polymer. In contrast, by using photochemical reactions instead of thermal reactions, not only spatiotemporal control becomes accessible, but also distinct reaction channels depending on the irradiation wavelengths . As photoreactive units can only be activated by photons of an energy matching the reactive excited state, extensive research efforts have been undertaken in the last decade to design systems of different chromophores that absorb and react only at certain wavelengths to allow an exclusive addressability solely by the choice of wavelengths .…”

Preparation of Cyclobutene Acetals and Tricyclic Oxetanes through Photochemical Tandem and Cascade Reactions

“…Among these compounds, 5fbalone was asolid product, and we obtained as ingle crystal that was suitable for X-ray diffraction (Figure 2). [18] As expected, the oxetane ring was planar, but both cyclobutanes were unusually flattened with Table 2: Preparation of angular tricyclic oxetanes through the triple photochemical cascade process. [a] [a] Reactionswere performed with 1 (1.5 mmol) and alkene (10 equiv or saturated (for ethylene)), in acetonitrile (50 mL) in asealed quartz tube at room temperature;irradiation was performed using a3 00 nm light source for aperiod of 40 h; yields are given for isolated products;d.r.was determined by 1 HNMR analysis of the crude reaction mixture.…”

“…Despite their inherent ring strain, these compounds displayed remarkable stability and could be isolated by column chromatography on silica gel. [18] As expected, the oxetane ring was planar, but both cyclobutanes were unusually flattened with [a] Reactionswere performed with 1 (1.5 mmol) and alkene (10 equiv or saturated (for ethylene)), in acetonitrile (50 mL) in asealed quartz tube at room temperature;irradiation was performed using a3 00 nm light source for aperiod of 40 h; yields are given for isolated products;d.r.was determined by 1 HNMR analysis of the crude reaction mixture. Among these compounds, 5fbalone was asolid product, and we obtained as ingle crystal that was suitable for X-ray diffraction ( Figure 2).…”

Development of an Alkyne Analogue of the de Mayo Reaction: Synthesis of Medium‐Sized Carbacycles and Cyclohepta[b]indoles

“…We surmized that the use of broad-band-emitting mediumpressure mercury vapor lamps were responsible for degradative secondary photochemical processes. [8] Therefore,w e started to investigate the alkyne-de Mayo reaction of the vinylogous ester 3b using narrow-band-emitting light sources (Table 1). TheU V/vis spectrum [9] of 3b in acetonitrile indicates as trong absorption maximum at 231 nm (e = 23 063 m À1 cm À1 ;a ssignable to the allowed p,p*t ransition) and aw eak, broad absorption maximum at 274 nm (e = 499 m À1 cm À1 ;a ssignable to the forbidden n,p*t ransition).…”