Diastereoselective Patemo-Buchi reaction

The enol ether double bond contained within the ds-fused dioxa-bicyclo[3.2.0]heptene photoadducts can also be oxidized, in a completely diastereoselective fashion, with mCPBA. Treatment of intermediate XXII, derived in one step from a Patemo-Buchi reaction between 3,4-dimethylfuran and benzaldehyde, with mCPBA results in the formation of intermediate XXIII. Once again, consecutive photocycloaddition and oxidation reactions furnish a highly oxygenated system that possesses five contiguous stereocenters, one of which is quaternary. Intermediate XXIII is particularly interesting because its constitution and its relative stereochemical relationships bear close homology to a portion of a natural product known as asteltoxin. 

The photo-Diels-Alder reaction of a-acetoTTapfithone 145 with the chiral a-enaminonitrile 146 yielded the cycloadduct 147 with almost complete diastere-oselectivity (Scheme 37) [91,92]. The intermediately formed biradical R is particularly stable owing to delocalization of the radical on the aromatic moiety and to a captodative effect on the enamine moiety. In analogy to the Patemo-Buchi reaction (see Scheme 7), the chiral induction occurred in two steps. In the first step, a chiral center is created at the a-position of the acyl group. In the second step of the diastereoselection, one of the two diasteromeric intermediates undergoes preferential cyclization to yield the final product 147, while the other one is decomposed to form the starting material [92]. 

Buschmann, H., Scharf, H. D., Hoffmann, N., Plath, M. W., Runsink, J. Chiral induction in photochemical reactions. 10. The principle of isoinversion a model of stereoselection developed from the diastereoselectivity of the Patemo-Buchi reaction. J. Am. Chem. Soc. 1989, 111, 5367-5373. 

Adam, W., Stegmann, V. R. Unusual Temperature Dependence in the cis/trans-Oxetane Formation Discloses Competitive Syn versus Anti Attack for the Patemo-Buchi Reaction of Triplet-Excited Ketones with cis- and trans-Cyclooctenes. Conformational Control of Diastereoselectivity in the Cyclization and Cleavage of Preoxetane Diradicals. J. Am. Chem. Soc. 2002,124, 3600-3607. 

Bach, T., Brummerhop, H. Unprecedented facial diastereoselectivity in the Patemo - Buchi reaction of a chiral dihydropyrrole-a short total synthesis of (+)-preussin. Angew. Chem., Int. Ed. Engl. 1999, 37, 3400-3402. 

According to the principle of isoinversion and generalization of the model of diastereoselection developed for the Patemo-Buchi reaction [47], the enantioselective protonation of photoenols can be rationalized, if we assume a preequilibrium between the photoenol [48] and a supramolecule formed by hydrogen bonding between the aminogroup from one or other enantio-face and the enol intermediate (Scheme 5). 

Inherent Diastereoselectivity Effect ofHydrogen Bonding on Diastereoselectivity of Patemo Btlchi Reaction Induced Diastereoselectivity Effect of Concentration on the Stereoselectivity of the Patemo Btlchi Reaction Effect of Temperature and Solvent Viscosity on the Stereoselectivity of the Paternb- Buchi Reaction... 

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