A new approach to spirosesquiterpenes of the acorane family

Abstract

Intramolecular [Z + 21 photocycloaddition of major intermediate which can be converted into the 3-( 1 ,5-dimethylhex-4-enyl)cyclohex-2-enone leads to a noracorenone system (5) , via a Norrish type I1 fission;

The switch-off method: rapid investigation of flow photochemical reactions

“…In the UV-B and C experiments, complete degradation of the photocycloaddition products was observed for long effective exposure times. The predominant formation for the less stable trans-fused cyclobutane isomer 5 is in accord with precedent [40][41][42] and has been explained. 43 The formation of 9 is precedented by some studies, 41 but not others.…”

“…The predominant formation for the less stable trans-fused cyclobutane isomer 5 is in accord with precedent [40][41][42] and has been explained. 43 The formation of 9 is precedented by some studies, 41 but not others. 40 Interestingly, when using UV-A light source a specific degradation of the cis-diastereoisomer 6 was observed after about 45 minutes of effective exposure time.…”

“…In this reaction a number of compounds can be formed, including the substituted cyclobutane in a [2 + 2] photocycloaddition between alkenes ( 5 and 6 ), cyclohex-2-enone dimerization products ( 7 and 8 ), and cyclohexane ( 9 ) formed via the Norrish type II fragmentation of compounds 5 or 6 . 40–43…”

“…In this reaction a number of compounds can be formed, including the substituted cyclobutane in a [2 + 2] photocycloaddition between alkenes (5 and 6), cyclohex-2-enone dimerization products (7 and 8), and cyclohexane (9) formed via the Norrish type II fragmentation of compounds 5 or 6. [40][41][42][43] The switch-off experiments were performed using UV-A, B, and C light sources and showed that maximum yields of cyclobutane products 5 and 6 of 65%, 30%, and 22% are obtained after 49, 25, and 20 minutes of effective exposure times, respectively for UV-A,…”

Stereoselective Intermolecular [2 + 2]-Photocycloaddition Reactions and Their Application in Synthesis

“…In combination with an intramolecular photocycloaddition it was applied to the synthesis of acorenone. 131 Path c gives access to compounds which are produced by a formal addition of two carbon fragments to the aand the b-position of a,b-unsaturated carbonyl compounds. If an enediol is used as alkene in the [2+2]-photocycloaddition an oxidative cleavage leads to 1,4-dicarbonyl compounds.…”