Samir Bondock

Temperature and Viscosity Dependence of the Spin‐Directed Stereoselectivity of the Carbonyl–Alkene Photocycloaddition

Table. Temperature dependence of the Paterno-Buchi reaktion of 2,3-dihydrofuran (2, 1M und 5M) mit 1a (1M) and 1b (1M and 5M) in n-hexane. temperature [°C] [K] 1/T [K] endo / exo for 2+1a endo / exo for 2+1b (1M) endo / exo for 2+1b (5M) +25 293 0.00341 88 : 12 45.3 : 54.7 47.6 : 52.4 0 273 0.00366 91 : 9 50.5 : 49.5 43.8 : 56.2 -10 263 0.00380 90 : 10 54.6 : 45.4 41.4 : 58.6 -15 258 0.00388 91 : 9 56.6 : 43.4 37.3 : 62.7 -25 248 0.00403 88 : 12 57.4 : 42.6 35.7 : 64.3 -32 241 0.00415 88 : 12 58.9 : 41.1 37.1 : 62.9 -42 231 0.00433 91 : 9 61.5 : 38.5 42.2 : 57.8 -52 221 0.00453 90 : 10 61.7 : 38.3 48.0 : 51.9 -61 212 0.00472 86 : 14 63.2 : 36.8 52.4 : 47.6 -72 201 0.00498 90 : 10 63.4 : 36.6 58.1 : 41.9 -78 195 0.00513 99 : 10 63.6 : 36.4 63.3 : 36.7

Stereoselective generation of vicinal stereogenic quaternary centers by photocycloaddition of 5-methoxy oxazoles to α-keto esters: synthesis of erythroβ-hydroxy dimethyl aspartates

The photocycloaddition of methyl pyruvate and methyl phenylglyoxylate, respectively, to 5-methoxy oxazoles bearing additional substituents at C-2 and C-4 leads to bicyclic oxetanes 2 and 3 with high to moderate (exo) diastereoselectivity that can be easily ring-opened to give bis-quaternary aspartic acid diester derivatives 4 and 5.

Photocycloaddition of 5-Methoxyoxazoles to Aldehydes and α-Keto Esters: A Comprehensive View on Stereoselectivity, Triplet Biradical Conformations, and Synthetic Applications of Paternò–Büchi Adducts

The photocycloaddition of carbonyl compounds (aldehydes and keto esters, respectively) with 5-methoxyoxazoles bearing substituents at C2 and C4 is described with respect to regio- and diastereoselectivity. In all cases the reactions proceed with excellent regioselectivity and with high to moderate (exo) diastereoselectivity independent of the nature of the excited carbonyl compound. The products can be easily ring-opened to give α-amino, β-hydroxy carboxylic acid derivatives.

Spin-dependent diastereoselectivity in the photocycloaddition of aldehydes to 2,2-dimethyl-2,3-dihydrofuran

The simple (non-induced) diastereoselectivity of the photocycloaddition of aliphatic as well as aromatic aldehydes to 2,2-dimethyl-2,3-dihydrofuran (1) was analyzed as a function of the substrate concentration (spin mapping) and rationalized in terms of optimal spin-orbit coupling controlled triplet biradical geometries.

Spin-imposed stereoselection in the photocycloaddition of (Z)- and (E)-cyclooctene to aliphatic aldehydes

The simple diastereoselectivity of the photocycloaddition of aliphatic aldehydes to (Z)- and (E)-cyclooctene was analyzed as a function of the substrate concentrations and applied to spin mapping.