Patemo-Buchi photochemical reaction

A patented synthesis by Doan et al. at GlaxoSmithKline used a Patemo-Buchi photochemical reaction to obtain acetal 33 in 96% yield, as shown in Scheme 8.35 Hydrogenation followed by acid-catalyzed cyclization resulted in a diastereomeric mixture of bis-THF alcohol ( )-ll. Formation of acetate 15, followed by lipase resolution resulted in the formation of the acetyl bis-THF, which was subsequently deprotected to afford the desired product (-)-ll in 98% ee.35... 

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. 

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... 

FMO calculations using PM3-C1 were used to investigate the regioselectivities obtained by the photochemical reactions between 2-pyridone and pcnta-2,4-dienoate.46 The hard and soft acid-base principle has been successfully used to predict product formation in Patemo-Buchi reactions.47 The 2 + 2-photo-cycloaddition of homobenz-valene with methyl phenylglyoxylate, benzyl, benzophenone, and 1,4-benzoquinone produced the corresponding Patemo-Buchi products.48 The photo-cycloaddition of acrylonitrile to 5-substituted adamantan-2-ones produces anti- and svn-oxetanes in similar ratios irrespective of the nature of the 5-substituent49... 

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... 

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. 

Forbidden according to symmetry rules [624g], [2+2]-cycloadditions are generally not concerted. When concerted [2+2]-cycloadditions do occur, the approach of both reagents should be supra-antarafacial. Usually, highly reactive species such as ketenes or ketenimminium salts are involved. Activation may be accomplished by adding Lewis acids or by irradiation (Patemo-Buchi reaction). In photochemical [2+2] -cycloadditions, the reaction takes place via an excited state and is symmetry-allowed. 

According to the Woodward-Hoflfmann rules, concerted thermal [2+2] cycloadditions are symmetry-forbidden, but should proceed via supra-antarafacial attack of the reactants. [2+2] cycloadditions of ketenes and related reactive intermediates generated in situ proceed by a stepwise mechanism. " Photochemical [2+2] cycloadditions are symmetry-allowed. Asymmetric [2+2] cycloadditions leading to 4-membered heterocycles, e.g. Staudinger reactions or Patemo-BUchi reactions, have been extensively studied in the past. 

The photochemical preparation of oxetanes is the domain of the Patemo-BUchi reaction, but only a few examples have been published where these heterocycles were prepared in the course of a Norrish/ Yang reaction. This is presumably due to the remarkable tendency of the corresponding 1,4-biradicals to undergo Norrish type 11 cleavage. Lewis and Turro explored the photochemical behavior of a-alkoxyacetophenones as early as 1970 and found that oxetanes are generally formed as minor products only. 

The photochemical [2 + 2]-cycloaddition reactions of carbonyl compounds with alkenes are known as the Paterno-Buchi reactions This reaction was first reported by the group of E. Patemo and G. Buchi on the reaction of benzaldehyde with 2-... 

---