Regioselective cyclization of m -acylaryl 1,1-dimethylpropargyl ethers giving 5-acyl-2,2-dimethyl-2 H -chromenes

A concise enantioselective synthesis and cytotoxic evaluation of the anticancer rotenoid deguelin enabled by a tandem Knoevenagel/conjugate addition/decarboxylation sequence

“…23 This alkyne 8 was then subjected to microwave conditions at 180 °C to yield the cyclized material 9 . Although there have been reports supporting the regiochemical outcome of this type of thermal cyclization reaction, 24-28 it does appear to go against conventionally held steric arguments which would dictate that the cyclization occur in the opposite direction. Therefore, the structure of 9 was confirmed by x-ray diffraction before moving onto the next step of the synthesis, with the results supporting the formation of the desired product (Scheme 2).…”

“…23 This alkyne 8 was then subjected to microwave conditions at 180 C to yield the cyclized material 9. Although there have been reports supporting the regiochemical outcome of this type of thermal cyclization reaction, [24][25][26][27][28] it does appear to go against conventionally held steric arguments which would Scheme 1 Retrosynthetic analysis of (À)-deguelin, featuring a late-stage oxidative alpha-arylation and a thiourea-catalyzed intramolecular cyclization. dictate that the cyclization occur in the opposite direction.…”

Total Synthesis of 7-Hydroxymurrayazolinine, Murrayamine D, and Mahanine via m-Nitro Group Activated Pyran Annulation

“…It would not only facilitate the final nitrene insertion reaction but also mask the free amine from the very beginning, so as to mitigate complications of the basicity of the nitrogen atom and its susceptibility to oxidation . We also assumed that the nitro group would activate the pyran annulation process (vide infra). ,, …”

Synthetic Study for Two 2H‐Chromenic Acids, 8‐Chlorocannabiorcichromenic Acid and Mycochromenic Acid.

“…As shown in Scheme 1, in previous papers, we reported two preparative methods for 2Hchromenes having a long side-chain at position 2. One (Method A) is the condensation of salicylaldehydes with isopropylidenemalonate giving the corresponding 2methyl-2H-chromene-2-acetates [5], and the other (Method B) is the thermal cyclization of phenyl propargyl ethers affording the corresponding 2H-chromenes [6]. We also reported a new approach to dl-cannabichromene via Jan-Feb 2006 29 Figure 1.…”

“…Method A; the condensation of 2-hydroxy-6-methoxy-4pentenylbenzaldehyde with isopropylidenemalonate [7]. A synthetic strategy for 8-chlorcannabiorcichromenic acid 1 via Method A is shown in Scheme 2, 1) preparation of 3-chloro-2-hydroxy-6-methoxy-4-methylbenzaldehyde (3), 2) condensation of 3 with methyl isopropylidenemalonate providing methyl 8-chloro-5-methoxy-2,7dimethyl-2H-chromene-2-acetate (4), 3) side-chain conversion to 8-chloro-2-methyl-2-(4-methyl-3-pentenyl)-5-(protected)oxy-2H-chromene (5), 4) Vilsmeier formylation affording the corresponding 6-carbaldehyde (6), 5) demethylation and oxidation leading to 1.…”