Photocycloaddition Reactions of 5,5‐Dimethyl‐3‐(3‐methylbut‐3‐en‐1‐ynyl)cyclohex‐2‐en‐1‐one

Abstract

Dedicated to Professor William C. Agosta on the occasion of his 75th birthdayThe title cyclohexenone 1d undergoes photodimerization selectively at the exocyclic C¼C bond to give a 1 : 1 mixture of 1,2-dialkynyl-1,2-dimethylcyclobutanes 6 and 7. On irradiation in the presence of 2,3-dimethylbuta-1,3-diene, 1d affords bicyclo[8.4.0]tetradeca-1,2,3,7-tetraen-11-one 9. This -formal -(6 þ 4)-cycloadduct undergoes quantitative isomerization to 3-cycloheptadienyl-2,5,5-trimethylcyclohex-2-enone 11 on treatment with basic silica gel.

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

“…[2 + 2] Photodimerization occurred to HH products with the relative configuration at the cyclobutane being trans ( rac - 197 ) or cis ( 198 ). 380 …”

Photocycloaddition Reactions of 2‐(Alk‐3‐en‐1‐ynyl)cyclohex‐2‐enones

“…As for the reaction with 2,3-dimethylbuta-1,3-diene, both excited 1 and 4 underwent primary binding between the exocyclic (olefinic) CH 2 group of the enone and a diene CH 2 Catom to afford biradicals 12 and 13, respectively. The fact that 12 then underwent a novel and unprecedented 1,10-cyclization [1], whereas 13 reacted further via -the expected -1,4-and 1,6-cyclization paths is most probably due to the different position of the acyl substituent in the intermediate pentynenyl radical moiety. Whereas in 12 delocalization extends to the C-atom adjacent to the C¼O group, and thus facilitates the 1,10-ring closure, this is not the case for -cross-conjugated -intermediate 13 (Scheme 4).…”

“…Introduction. -Quite recently, we have reported [1] that the (photo)reactivity of 3-alkynylcyclohex-2-enones was completely altered by extending the conjugation of the side chain at C(3) by an additional C¼C bond. Indeed, we observed that 5,5-dimethyl-3-(3-methylbut-3-en-1-ynyl)cyclohex-2-enone (1) a) undergoes photocyclodimerization selectively at this -additional -exocyclic C¼C bond to afford 2, and b), in the presence of 2,3-dimethylbuta-1,3-diene, affords a novel [6 þ 4] photocycloadduct 3 containing a buta-1,2,3-triene moiety (Scheme 1).…”

“…-Under photodimerization conditions, i.e., irradiation of 0.5m solutions, cyclohexenones 4 behave very similarly to 1 by reacting almost exclusively at the exocyclic C¼C bond. The assignment of the trans-configuration to the majordiastereoisomer 6 was based on the analysis of the vicinal coupling constants of the AA'XX' pattern of the two adjacent CH 2 groups in the cyclobutane ring [1] and the chemical shifts of the Me groups in the 13 C-NMR spectra, in which the Me C-atoms of the trans-diastereoisomer resonated at lower field by ca. 5 ppm [3].…”

Photocyclodimerization of 5‐Methyl‐2H‐pyran‐3(6H)‐one

“…Both enantioselective GC analysis [4] as well as CI-MS [5] can be helpful, but only if these dimers are stable under these conditions. In a recent publication [6], we have proposed for the first time to use 13 C-NMR data for the differentiation between the (regioisomeric) photodimers of 3,5,5-trimethylcyclohex-2-enone (1). We have now extended such studies to photocyclodimers of 3-Me-substituted oxacyclohex-2-enones (¼ dihydropyranones) 2 -4.…”