Oxetane, synthesis

The scope of the Patemo-Buchi cycloaddition has been widely expanded for the oxetane synthesis from enone and quinone acceptors with a variety of olefins, stilbenes, acetylenes, etc. For example, an intense dark-red solution is obtained from an equimolar solution of tetrachlorobenzoquinone (CA) and stilbene owing to the spontaneous formation of 1 1 electron donor/acceptor complexes.55 A selective photoirradiation of either the charge-transfer absorption band of the [D, A] complex or the specific irradiation of the carbonyl acceptor (i.e., CA) leads to the formation of the same oxetane regioisomers in identical molar ratios56 (equation 27). 

There are a wide variety of other synthetic methods for the preparation of oxetanes however, most of these are not very general. They frequently require starting materials which are difficult to prepare, and rarely give high yields (never as high as the better photochemical preparations). It is clear then that in comparison with the alternative methods of oxetane synthesis, the photocycloaddition reaction is more generally useful and convenient. This synthetic utility justifies a brief description of experimental conditions. 

Mildly basic to neutral conditions for the ring closure of 1,3-halohydrins include tetra-phenylantimony methoxide as an effective non-basic reagent for oxetane synthesis from 1,3-bromohydrins (90S106). The salts of (3-halo acids cyclize in ionizing media to oxetan-2-ones, as do (3-diazonium carboxylates (64HC(l9-2)787). Thietanes are obtained analogously. 

Widman-Stoermer synthesis, 3, 43 Wild-fire toxin, 7, 249 Willardiine, synthesis, 3, 146 Willgerodt reaction thiophene synthesis by, 4, 883 Williamson reaction oxetane synthesis by, 7, 390-391 Withasomnine occurrence, 5, 302 Wittig reaction crown ethers and, 7, 759 Wittig-Homer reactions crown ethers and, 7, 759 Wolff rearrangement oxirenes in, 7, 120, 126... 

A. Vargas-Berenguel, F. Santoyo-Gonzalez, J. A. Calvo-Asin, F. G. Calvo-Flores, J. M. Exposito-Lopez, F. Hernandez-Mateo, J. Isac-Garcia, and J. J. G. Martinez, Synthesis of 6-deoxyheptose derivatives via cyclic sulfates and oxetanes, Synthesis, (1998) 1778-1786. 

Sakamoto et al. also demonstrated an absolute oxetane synthesis in the solid-state photolysis of Y-( ,(3-unsaturatcd carbonyl)benzoylformamides 43. [28] The X-ray analysis of Y-isopropyl substituted imide 43a revealed that the crystal system was monoclinic and the space group P2. Crystals of 43a were powdered and photolyzed at 0°C. The imide undergoes the [2+2] cycloaddition to afford the bicyclic oxetane 44a, which is a mixture of diastereomers, namely, syn- and anh-isomers at the C-7 position. In this reaction optically active. syn-oxctanc 44a with 37% ee (84% chemical yield) and racemic anti-44a were obtained. The solid-state photoreaction proceeded even at -78°C, and optically active syn-44n which showed ee value as high as >95% ee, (conv 100%, chemical yield 89%) was formed in a higher diastereomeric ratio (syn/anti = 6.5). Under identical conditions A-bcnzyl substituted 43b was irradiated in the solid state. 

Solid-state photochemistry absolute asymmetric oxetane synthesis from an achiral acyclic imide using die chiral crystal environment, J. Org. Chem., 58, 3476-3477. (b) Sakamoto, M., Takahashi, M., Fujita, T.,... 

Ring Synthesis Classified by Number of Ring Atoms 2.05.9.1 Oxetane Synthesis by Single C-0 Bond Formation... 

The photochemical reaction of carbonyl compounds and alkenes, which is referred to as the Paterno-Buchi (PB) reaction, was developed in 1909 [13], and is currently one of the most widely used methods for oxetane synthesis (Scheme 7.4). As exemplified in the PB reaction of benzophenone with 2-methylpropene [14], a selective formation of the oxetane is possible even when the photochemical reaction involves highly unstable molecules that is, the excited state of carbonyls. Due to its synthetic importance and mechanistic interest, the PB reaction is the most extensively studied synthetic method for oxetanes. Thus, several extensive reviews describing the PB reaction have been published since 1968, and the reader is directed towards these for further information [15]. In this chapter, methods that allow for the control of the regioselective and stereoselective formation of synthetically important oxetanes will be described. 

In this chapter, recent developments in the regioselective, site-selective, and stereoselective preparation of oxetanes have been summarized. The relative nudeophilicity of the alkene carbons was seen to be important for regioselectivity, in addition to the well-known radical stability rule. Likewise, the three-dimensional structures of the triplet 1,4-biradicals were seen to play an important role in stereoselectivity. For photochemical reactions that proceed via radical ion pairs, the spin and charge distributions are crucial determinants of regioselectivity. It follows that the concepts used in selective oxetane synthesis should stimulate future investigations into the mechanistically and synthetically fascinating Paterno-Bitchi-type reactions. 

A generally applicable oxetane synthesis (e.g., 100 101) can be achieved by the anionic ring contraction of cyclic acetals fused to butanolide using organolithium reagents (Scheme 53) <2004SL651, CHEC-III(2.05.10.2)352>. 

Morris, T. H., Smith, E. H., Walsh, R. Oxetane synthesis. Methyl vinyl sulfides as new traps of excited benzophenone in a stereoselective and regiospecific Paterno-Buchi reaction. J. Chem. Soc., Chem. Common. 1987, 964-965. 

Some of the reactions included have been discussed in other review articles on the photochemistry of heterocyclic compounds,1,7 dimerization reactions,l9,118,119 photochemical oxetane synthesis,6 and photochemical addition reactions.120... 

Oxetane synthesis. Two new syntheses of oxetane using this reagent have been reported (equations 1 and 11). A third synthesis employs tributyl-ethoxy tin (111). 

Synthetic approaches to fluorinated p-lactones (oxetane-2-ones) are very similar to oxetane synthesis. Usually p-lactones are prepared either by cycloaddition of ketenes to aldehydes or ketones or by cyclodehydration of p-hydroxycarboxylic acids. 

Oxetane synthesis through the Patemo—Biichi reaction 13MOL11384. 

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