Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

Abstract

The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4, whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin.

Brønsted‐Säure‐Katalyse der [2+2]‐Photocycloaddition von Enondithianen bei Bestrahlung mit sichtbarem Licht

“…[1] Sie ermçglicht den gleichzeitigen Aufbau von zwei C-C-Bindungen und von bis zu vier stereogenen Zentren. Damit ähnelt sie der thermischen [4+ +2]-Cycloaddition, der DielsAlder-Reaktion, die einen ähnlich hohen Anstieg der Komplexitäte rlaubt.…”

Conformationally Driven Two- and Three-Photon Cascade Processes in the Stereoselective Photorearrangement of Pyrroles

“…An optimization study showed that a ketone in the 2-position of the pyrrole was essential to enable lactam formation (Table 3, entries [1][2][3][4][5] and that a second ketone was actually deleterious to the process (entry 6). Although yields averaged around 50%, this in itself is quite remarkable as intense, high energy 254 nm UV light is used and the successful formation of 22 relies on 3-successive and independent photon mediated events.…”

Photochemical [2+2] cycloaddition reaction of enone derivatives with 2-silyloxy-1H-pyrrole derivatives

“…The strained cyclobutane [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] and oxetane [21][22][23] structures are important in organic synthesis. After Ciamician discovered the first example of photochemical [2+2] cycloaddition reaction, 24 Paternò, following Ciamician, reported the first photochemical [2+2] oxetane formation reaction using light irradiation.…”