https://pubs.rsc.org/en/content/articlepdf/2019/NP/C8NP00092A

Marine natural products.

The application of (S)-1,10-binaphthyl-2,20-diol as NMR chiral solvating agent (CSA) for omeprazole, and three of its analogs (lanso-, panto-, and rabe-prazole) was investigated. The formation of diastereomeric host–guest complexes in solution between the CSA and the racemic substrates produced sufficient NMR signal splitting for the determination of enantiomeric excesses by Hor F-NMR spectroscopy. Using of hydrophobic deuterated solvents was mandatory for obtaining good enantiodiscrimination, thus suggesting the importance of intermolecular hydrogen bonds in the stabilization of the complexes. The method was applied to the fast quantification of the enantiomeric purity of in-process samples of S-omeprazole. Chirality 00:000–000, 2009. VC 2009

The assignment of absolute configuration by NMR

The [2 + 2] photocycloaddition is undisputedly the most important and most frequently used photochemical reaction. In this review, it is attempted to cover all recent aspects of [2 + 2] photocycloaddition chemistry with an emphasis on synthetically relevant, regio-, and stereoselective reactions. The review aims to comprehensively discuss relevant work, which was done in the field in the last 20 years (i.e., from 1995 to 2015). Organization of the data follows a subdivision according to mechanism and substrate classes. Cu(I) and PET (photoinduced electron transfer) catalysis are treated separately in sections 2 and 4, whereas the vast majority of photocycloaddition reactions which occur by direct excitation or sensitization are divided within section 3 into individual subsections according to the photochemically excited olefin.

http://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.5b00723

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

Photochemical reactions contribute in a significant way to the existing repertoire of carbon-carbon bond-forming reactions by allowing access to exceptional molecular structures that cannot be obtained by conventional means. In this Review, the most important photochemical transformations that have been employed in natural product synthesis are presented. Selected total syntheses are discussed as examples, with particular attention given to the photochemical key step and its stereoselectivity. The structural relationship between the photochemically generated molecule and the natural product is shown, and, where necessary, the consecutive reactions in the synthesis are illustrated and classified.

Photochemical reactions as key steps in natural product synthesis

Cyclizations of N-acyliminium ions.

Preparation of an 8‐Membered Ring via Intramolecular (2 + 2) Photocycloadduct: Formal Total Synthesis of (.+‐.)‐Precapnelladiene.

The 1,3-dipolar cycloaddition of nitrile oxides to 2-X-bicyclo[2.2.2]oct-5-enes (X=O, NMe, S, SO2) were investigated together with acyclic and alicyclic analogues. The regioselectivity in an exo-attack was controlled by the heteroatom present at an allylic position —a remote attack was predominant in the cases of O and SO2 but a vicinal attack in those of NMe and S— and the results were rationalized from the electronic nature of the heteroatom, X. In an endo-attack, a remote attack was observed in every case and the dipole-dipole repulsion between X and the oxygen of the nitrile oxide was considered to be a predominant factor. The steric environment around the heteroatom controled the facial-selectivity.

Regio- and Facial-Selective Effects of Allylic Heteroatoms in 1,3- Dipolar Cycloaddition of a Nitrile Oxide.

The irradiation of 5,5-dimethyl-3-(4-methyl-3-pentenyloxy)-2-cyclohexenone gave regioselectively, 6,6,10,10-tetramethyl-2-oxatricyclo[5.4.0.01,5]undecan-8-one, while, that of 5,5-dimethyl-3-[(3-methylcyclohexenyl)methoxy]-2-cyclohexenone afforded, regio- and stereoselectively, 1,5,5-trimethyl-8-oxatetracyclo[8.3.1.02,7.01,5]tetradecan-3-one.

Intramolecular (2 + 2) photocycloaddition of the 3‐(3‐butenyloxy)‐2‐cyclohexenone system

Regioselective Effects of the Allylic Heteroatoms in 1,3-Dipolar Cycloaddition of Nitrones to Several Allyl Derivatives.

1,3-Dipolar cycloaddition of nitrones on several allyl silanes, allyl ethers, and allyl alcohol was investigated. The silicon atom in dipolarophiles controlled the regioselectivity in favor for 5-(silylmethyl)isoxazolidines, while the oxygen atom for 4-(alkoxymethyl)isoxazolidines.

Yoshinobu Inouye

Papers

Preparation of an 8‐Membered Ring via Intramolecular (2 + 2) Photocycloadduct: Formal Total Synthesis of (.+‐.)‐Precapnelladiene.

Regio- and Facial-Selective Effects of Allylic Heteroatoms in 1,3- Dipolar Cycloaddition of a Nitrile Oxide.

Intramolecular (2 + 2) photocycloaddition of the 3‐(3‐butenyloxy)‐2‐cyclohexenone system

Regioselective Effects of the Allylic Heteroatoms in 1,3-Dipolar Cycloaddition of Nitrones to Several Allyl Derivatives.

The Regioselective Effect of the Allylic Silicon or Oxygen Atom in 1,3-Dipolar Cycloaddition of Nitrones.