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Buchi reaction

The Patemo-Buchi reaction " is the photo-eatalyzed eJeetrocyeJization of a carbonyl 1 with an alkene 2 to form polysubstituted oxetane ring systems 3. [Pg.44]

The most valuable characteristic of the Patemo-Buchi reaction is the ability to set multiple stereocenters in one reaction and the development of diastereocontrolled reactions has been a major theme of research concerning this reaction. Stereocontrol can be envisioned to spring from either the carbonyl or the alkene and be controlled by either the substrate directly or by a chiral auxiliary. Little success has been achieved in substrate-induced selection by the carbonyl the most successful results were produced by... [Pg.46]

The oxetane functional unit is a rare but occurring group in natural products and appears both as end products as well as synthetic intermediates. Patemo-Buchi reactions can be used to insert oxetanes directly into biologically active compounds, as in the example... [Pg.47]

Two different alkenes can be brought to reaction to give a [2 -I- 2] cycloaddition product. If one of the reactants is an o, /3-unsaturated ketone 11, this will be easier to bring to an excited state than an ordinary alkene or an enol ether e.g. 12. Consequently the excited carbonyl compound reacts with the ground state enol ether. By a competing reaction pathway, the Patemo-Buchi reaction of the 0, /3-unsaturated ketone may lead to formation of an oxetane, which however shall not be taken into account here ... [Pg.78]

In general however the various possible reaction pathways give rise to formation of a mixture of products. The type I-cleavage reaction is only of limited synthetic importance, but rather an interfering side-reaction—e.g. with an attempted Paterno-Buchi reaction, or when an aldehyde or ketone is used as sensitizer in a [2 -I- l -cy do addition reaction. [Pg.215]

The photochemical cycloaddition of a carbonyl compound 1 to an alkene 2 to yield an oxetane 3, is called the Patemo-Buchi reaction - This reaction belongs to the more general class of photochemical [2 + 2]-cycloadditions, and is just as these, according to the Woodward-Hofmann rules, photochemically a symmetry-allowed process, and thermally a symmetry-forbidden process. [Pg.221]

In addition to the intermolecular Paterno-Buchi reaction, the intramolecular variant has also been studied the latter allows for the construction of bicyclic structures in one step. For example the diketone 8 reacts quantitatively to the bicyclic ketone 9 ... [Pg.222]

Although the Paterno-Buchi reaction is of high synthetic potential, its use in organic synthesis is still not far developed. In recent years some promising applications in the synthesis of natural products have been reported. The scarce application in synthesis may be due to the non-selective formation of isomeric products that can be difficult to separate—e.g. 6 and 7—as well as to the formation of products by competitive side-reactions such as Norrish type-I- and type-II fragmentations. [Pg.222]

Scheme 2. The Paterno-Buchi reaction as a photochemical aldol equivalent. Scheme 2. The Paterno-Buchi reaction as a photochemical aldol equivalent.
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. [Pg.321]

Typical chemical reactions of photoexcited aldehydes and ketones are cleavage reactions, usually designated as Norrish Type I [equation (54)], II [equation (55)] and III [equation (56)], hydrogen abstraction [equation (57)] and cycloadditions, such as the Paterno-Buchi reaction [equation (58)]. Of these, Norrish Type II cleavage and the related... [Pg.104]

Ordinary aldehydes and ketones can add to alkenes, under the influence of UV light, to give oxetanes. Quinones also react to give spirocyclic oxetanes. This reaction, called the Patemo-BUchi reaction,is similar to the photochemical dimerization of alkenes discussed at 15-61.In general, the mechanism consists of the addition of an excited state of the carbonyl compound to the ground state of the alkene. Both singlet (5i) and n,n triplet states have been shown to add to... [Pg.1249]

Photocycloaddition Reactions of Carbonyl Compounds and Alkenes. Photocycloaddition of ketones and aldehydes with alkenes can result in formation of four-membered cyclic ethers (oxetanes), a process often referred to as the Paterno-Buchi reaction.196... [Pg.548]

Some other examples of Paterno-Buchi reactions are given in Scheme 6.11. [Pg.552]

Scheme 1 UV-light induced formation of the two major photo lesions in DNA. T=T cyclobutane pyrimidine dimer. (6-4)-photo product (6-4)-lesion, formed after ring opening of an oxetane intermediate, which is the product of a Paterno-Buchi reaction... Scheme 1 UV-light induced formation of the two major photo lesions in DNA. T=T cyclobutane pyrimidine dimer. (6-4)-photo product (6-4)-lesion, formed after ring opening of an oxetane intermediate, which is the product of a Paterno-Buchi reaction...
Flavin-cyclobutane pyrimidine dimer and flavin-oxetane model compounds like 1-3 showed for the first time that a reduced and deprotonated flavin is a strong photo-reductant even outside a protein environment, able to transfer an extra electron to cyclobutane pyrimidine dimers and oxetanes. There then spontaneously perform either a [2n+2n cycloreversion or a retro-Paternd-Buchi reaction. In this sense, the model compounds mimic the electron transfer driven DNA repair process of CPD- and (6-4)-photolyases. [Pg.212]

In 1954 this reaction was more extensively investigated by Buchi,. Inman, and Lipinsky,(81) who confirmed the oxetane structure of the photoproduct. To credit their initial work on this interesting reaction, it commonly is referred to as the Paterno-Buchi reaction. [Pg.98]

In the general context of donor/acceptor formulation, the carbonyl derivatives (especially ketones) are utilized as electron acceptors in a wide variety of reactions such as additions with Grignard reagents, alkyl metals, enolates (aldol condensation), hydroxide (Cannizzaro reaction), alkoxides (Meerwein-Pondorff-Verley reduction), thiolates, phenolates, etc. reduction to alcohols with lithium aluminum hydride, sodium borohydride, trialkyltin hydrides, etc. and cyloadditions with electron-rich olefins (Paterno-Buchi reaction), acetylenes, and dienes.46... [Pg.212]

A very complex group of observations and speculations has been presented in Section IV. It might almost seem illogical to apply a single theoretical approach to so diverse a set of reactions, but the utility of PMO theory for correlating the several aspects of Paterno-Buchi reactions has already been demonstrated. 38-39> The newer results to be presented below will help to confirm the idea that PMO theory gives a unified useful theoretical picture for the majority of [2+2] photocycloaddition reactions. First, however, the many approximations and postulates inherent in this work should be made clear. [Pg.156]

Oxetanes are the cycloadducts from a carbonyl compound and an olefin. This one step photochemical formation of a four membered ring heterocycle has been named the Paterno-Buchi reaction 489a> b). Oxetanes are important synthetic intermediates as they can fragment into the carbonyl-olefin pair by which they were not formed (a so termed carbonyl-olefin metathesis). Two examples of such oxetan cracking reactions are shown below in (4.76)490) and in (4.77)491) in this last example the oxetane was used as a precursor for the pheromone E-6-nonenol,... [Pg.66]

B. Paterno-Buchi Reactions Employing Conjugated Dienes. 297... [Pg.263]

The [2+2]-photocycloaddition of carbonyl groups with olefins (Paterno-Buchi reaction) is one of the oldest known photochemical reactions and has become increasingly important for the synthesis of complex molecules. Existing reviews have summarized the mechanistic considerations and defined the scope and limitations of this photocycloaddition73. Although this reaction likely proceeds via initial excitation of the carbonyl compound and not the excited state of the diene, the many examples of this reaction in natural product synthesis justify inclusion in this chapter. [Pg.297]


See other pages where Buchi reaction is mentioned: [Pg.133]    [Pg.294]    [Pg.302]    [Pg.463]    [Pg.1]    [Pg.45]    [Pg.46]    [Pg.46]    [Pg.47]    [Pg.221]    [Pg.68]    [Pg.193]    [Pg.697]    [Pg.143]    [Pg.297]    [Pg.298]   


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