Patemo stereoselectivity

In the context of photoinduced [2 -I- 2] cycloadditions, the reaction of an olefin with a carbonyl center, known as the Patemo-Biichi reaction, has to be mentioned. The resulting oxetanes are thereby produced with high regioselectivity and stereoselectivity. 

First reported in 1909, the photochemical [2+2] cyclization between alkenes and carbonyl compounds, known as the Patemo-Biichi reaction, is one of the most commonly used methods of synthesizing oxetanes. The scope of the reaction is however limited and only occurs readily between electron-rich alkenes and electron-poor carbonyls. The importance of the reaction is that, with careful selection of alkenes and carbonyl compounds, high regio- and stereoselectivities can be achieved (see CHEC(1984) and CHEC-II(1996) for previous examples) < 1984CHEC(7)363, 1996CHEC-II(1)721>. 

Another open question is related to the diastereoselectivity of the reaction. We have shown that Adam s rule cannot be used to explain the observed stereoselectivity in the reaction with 2-furylmethanol derivatives. If Adam s hypothesis does not work, the diastereoselectivity of the Patemo-Biichi reaction with allylic alcohols remains to be explained. 

N Plath, M.W., and Runsink, J. (1989) Chiral Induction in photochemical reactions 10. The principle of isoinversion A model of stereoselection developed from the diastereoselectivity of the Patemo-Biichi reaction. Journal of the American Chemical Society, 111, 5367-5373. 

Related Reactions. The photochemistry (Patemo-Biichi reactions) of the achiral oxazoline (7) has been studied. The analogous urethane (8), which is chiral by attachment of an apocam-phanoyl group, shows an intriguing stereoselectivity pattern in its reaction with electrophiles. For another case of an oxidative decarboxylation as a key step in the application of the SRSC (selfregeneration of stereogenic centers) principle, see the preparation of the dihydropyrimidone (9) from aspartic acid. ... 

The synthesis of oxetanes from alkenic precursors has been demonstrated and the range and scope of Patemo-Biichi photocycloadditions are broad. In general, both the reaction regioselectivity and stereoselectivity can often be predicted by considering the reaction mechanism (Section 2.4.2) for example, the directing effects of alkene substituents are readily imderstood. Synthetic applications are numerous owing to the rtq>id stereocontrolled assembly of multifimctional targets. 

Several reports of transannular Patemo-Buchi photocyclizations have been documented. Mihai-lovi has demonstrated that cholesterol can be hydroxylat indirectly but stereoselectively at C-1 through a Patemo-BUchi reaction, thus allowing access to vitamin D3 analogues. Scheme 21 illustrates the procedure in which the a-b ring fusion of alcohol (199) was first cleaved via photochemical hypoiodite... 

A model for stereoselection that has been developed from the analyses of face-discriminating Patemo-Biichi reactions has been reported by Scharf and coworkers. Isoselective relationships were ob-... 

The Patemo-Buchl reaction of furan and various aldehydes was shown to be a highly stereoselective photochemical version of the aldol reaction by S.L. Schreiber and co-workers in which the furan serves as an enolate equivalent. This strategy was applied to the total synthesis of the antifungal metabolite (+)-avenaciolide. The photocycloaddition of nonanal with excess furan proceeded in nearly quantitative yield, and the two out of the three required stereocenters were created in a single step. The photocycloadduct was first hydrogenated then hydrolyzed under acidic conditions. 

Similar to the regioselectivity of the Patemo Biichi reaction, there is no general rule for stereoselectivity covering all reported examples. Several features must be considered 1) multiplicity, i.e. concerted or nonconcerted, 2) stability of 1,4-diradicals and their competing decay processes, 3) hyperconjugation effects, 4) organized medium etc. 

Schreiber and co-workers have detailed the utility of the Tietze reagent, 2-formylmalondialdehyde, in stereoselective [4 + 2] cycloadditions with the Patemo-Buchi photoadducts derived from furan and aldehydes for use in the stereoselective assemblage of highly oxygenated aliphatic substrates [Eq. (13)].98... 

The Patemo-Buchi reaction is one of the more predictable photocycloaddition reactions. Regiocontrol of the photoproduced oxetane is a function of the stepwise addition of the carbonyl chromophore to the alkene [30]. In the case of electron-rich alkenes, excitation of the carbonyl group produces a triplet species that adds to the alkene. The product regioselectivity is a result of addition that generates the most stable biradical, and the triplet lifetime of the intermediate biradical allows for substantial stereoselectivity prior to closing (see Scheme 2). Electron poor alkenes are more likely to undergo cycloaddition with carbonyl groups directly from an exciplex [31]. 

The Patemo-Buchi reaction has also received considerable attention in the past several years. Stereoselectivity in this reaction seems to be a function of both steric and electronic effects. In some cases, one is dominant over the other, but both usually play a part. For example, in the addition of disubstituted alkenes to 5-substituted adamantanones, electronics plays a more major part than sterics... 

This idea is supported by the work of Griesbeck, who has published several examples of stereoselective Patemo-Biichi reactions. The irradiation of... 

An interesting extension of the Patemo-Biichi reaction is the photochemical formation of thietanes. A recent example [125] of stereoselective thietane formation shows that sterics play a large role in the selectivity. Silyl thioketone 131 (see Scheme 48) was irradiated in the presence of several electron-poor alk-enes, which showed greater than a 12 1 propensity for the larger group on... 

Reviews of the Patemo-Buchi photocycloaddition reaction for the synthesis of mono- and bi-cyclic oxetanes <00SL1699> and the stereoselective synthesis of oxetanones are available... 

Oxygen atoms in the tetrahydrofuran rings embedded in inositol-based tris(spirotetrahydrofuranyl)ionophores were useful as chelation sites towards selective alkali metal ion binding and as a result rodlike supramolecular ionic polymer frameworks were prepared and analyzed in this study <01JA4974>. The temperature and viscosity dependence of the spin-directed stereoselectivity of the Patemo-Buchi photocycloaddition reactions between 2,3-dihydrofuran and benzaldehyde were studied <01 AG(E)4684>. 

Abe M, Terazawa M, Nozaki K, Masuyama A, Hayashi T (2006) Notable temperature effect on the stereoselectivity in the photochemical [2+2] cycloaddition reaction (Patemo-Biichi reaction) of 2,3-dihydrofuran-3-ol derivatives with benzophenone. Tetrahedron Lett 46 2527-2530... 

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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