Chemoenzymatic and electrochemical oxidations in the synthesis of octahydroisoquinolines for conversion to morphine. Relative merits of radical vs. acid-catalyzed cyclizations

Benefits of Unconventional Methods in the Total Synthesis of Natural Products

“…For example, anodic oxidation of 77 under the conditions similar to those used for pymetrozine produced a mixture of hemiaminals 78 that were then cyclized under Lewis acidic conditions to octahydroisoquinoline 79 , an intermediate in one of our approaches to morphine. 44 Electrochemical reduction of vinyl bromide in 80 was accomplished with mercury pool cathode and proved the method of choice for generation of many intermediates used for the synthesis of inositols. 45 A highly selective reduction of vinyl iodide over vinyl bromide in 81 was also achieved, as was oxidation of the diene diol 82 to the syn epoxide 84 (via the intermediate bromohydrin 83 ).…”

“…In 1978, our group initiated a program aimed at a general synthesis of natural products containing five-membered rings. The program was successful, as evidenced by the attainment of many triquinane terpenes, such as hirsutene (32), 22 isocomene (38), 23 pentalenic acid (41), 24 and most notably, a 14-step synthesis of the racemate of retigeranic acid (44), 25 still standing as the shortest one to date. The preparation of terpenoids the size of retigeranic acid (44) or aphidicolin (29) may very well define the limits of the utility of FVP, as substrates of higher molecular weight may not be fully vaporized, even under very high vacuum.…”

“…The program was successful, as evidenced by the attainment of many triquinane terpenes, such as hirsutene (32), 22 isocomene (38), 23 pentalenic acid (41), 24 and most notably, a 14-step synthesis of the racemate of retigeranic acid (44), 25 still standing as the shortest one to date. The preparation of terpenoids the size of retigeranic acid (44) or aphidicolin (29) may very well define the limits of the utility of FVP, as substrates of higher molecular weight may not be fully vaporized, even under very high vacuum. Heteroatom variants of the rearrangement (oxa-, aza-, and thia-) were also employed in total synthesis of natural products, some of which are shown in Figure 5.…”

Electrochemical strategies for C–H functionalization and C–N bond formation

“…Okimoto and coworkers have also demonstrated that Shonotype oxidation of various amine-containing motifs carrying pendant nucleophiles can be employed to access a diverse set of heterocyclic compounds through intramolecular C-C or C-X bond formation processes (Scheme 11). [153][154][155][156][157][158][159] Using a combination of NaOMe and KI as supporting electrolyte in MeOH proved to be the optimal for affecting electrochemical oxidation and subsequent intramolecular cyclization of tetrahydro(iso)quinolines 42 and 44 housing pendant alcohol or amine groups.…”

A Convenient Access to Functionalized Oxazol-2-One-5-Carboxylates from β-Aminoalcohols Through NBS-Light Mediated Oxidation of Cis- or Trans-N-Alkyloxazolidinones

“…Some of them serve as excellent precursors for various nitrogencontaining heterocyclic compounds of synthetic and biological interest [56][57][58][59][60][61]. However, there are very few reports in the literature for the conversion of oxazolidin-2-ones into oxazol-2-ones [62][63][64][65][66][67][68]. Among them, the most common transformations of N-alkyloxazolidin-2-ones into oxazol-2-ones are catalytic tautomerization [62], β-selective Pdcatalyzed oxidative Heck reaction [64] and chlorination with sulfuryl chloride followed by reductive dehalogenation [65].…”