2-Isopropylbenzimidazole and 2-methylbenzimidazole as bulky proton sources: Stereoselective protonation and application to the synthesis of γ- and δ-lactones

Divergent Asymmetric Synthesis of Panowamycins, TM‐135, and Veramycin F Using C−H Insertion with Donor/Donor Carbenes

“…The requisite homoallylic alcohol 29 was difficult to access as a single enantiomer by reported methods. [31][32][33][34][35] As proof of concept and to confirm the relative stereochemistry of 1 and 2, a racemic synthesis was performed from commercially available (�)-2-methyl-but-3enoic acid (28). Hydrazone (�)-30 was accessed in three steps, as above (Figure 3), in similar efficiency.…”

“…Taking these challenges into account, the Wacker oxidation strategy was then pursued, as it allows for certainty of configuration at a pre‐installed C12 stereogenic center (Figure 6). The requisite homoallylic alcohol 29 was difficult to access as a single enantiomer by reported methods [31–35] . As proof of concept and to confirm the relative stereochemistry of 1 and 2 , a racemic synthesis was performed from commercially available (±)‐2‐methyl‐but‐3‐enoic acid ( 28 ).…”

Recent advances in the synthesis of insect pheromones: an overview from 2013 to 2022

“…Fig. 9 shows the pheromones of Osmoderma eremita (Col., Cetoniidae): 194, 174,175 Nasonia vitripennis (Hym., Pteromalidae): 195, 176 Bactrocera tsuneonis (Dip., Tephritidae): 196, 177 Popillia japonica (Col., Scarabaeidae): (R)-197 and Anomala osakana (Col., Scarabaeidae): (S)-197, 178 Rhagoletis batava (Dipt., Tephritidae): 198, 179 Macrocentrus grandii (Hym., Braconidae): 199, 180 Vespa orientalis (Hym., Vespidae): 200, [181][182][183][184] Culex spp. (Dip., Culicidae): 201, [185][186][187][188][189] Phoracantha synonyma (Col., Cerambycidae): 202, 190 Silvestritermes minutus (Iso., Termitidae): 203, 191 Heliconius erato phyllis (Lep., Nymphalidae): 204 (anti-aphrodisiac).…”

Total Synthesis of PF1163B

“…5 Therefore, we examined the protonation with 2-alkylated benzimidazoles (Table 2). 6,7 When NH 4 Cl was employed as a proton source, no stereoselectivity was observed (Table 2, entry 1). 2-Methylbenzimidazole, reported as an excellent proton source in the total synthesis of mycocerosic acid, gave the reduced products in 64% as a 4.4:1 mixture with the desired isomer 12 as a major isomer (entry 2).…”

“…Therefore, we employed 2-isopropylbenzimidazole as the best proton source in the Birch reduction of 4. 7 Synthesis of the polyketide segment 3 and completion of the total synthesis is described in Scheme 4. DIBAL reduction of 4 directly gave aldehyde 13, which was subjected to Horner-Wadsworth-Emmons reaction 8 with 14 gave α,β,γ,δ-unsaturated ester 15.…”