Reactions with oxetanes

A-Substituted pyrroles, furans and dialkylthiophenes undergo photosensitized [2 + 2] cycloaddition reactions with carbonyl compounds to give oxetanes. This is illustrated by the addition of furan and benzophenone to give the oxetane (138). The photochemical reaction of pyrroles with aliphatic aldehydes and ketones results in the regiospecific formation of 3-(l-hydroxyalkyl)pyrroles (e.g. 139). The intermediate oxetane undergoes rearrangement under the reaction conditions (79JOC2949). 

Some ketones undergo a cycloaddition reaction with alkenes to form oxetanes ... 

Bis(3-nitrofurazanoxymethyl)oxetane 221 was synthesized in 52% yield by base-promoted ring closure of the corresponding 3-hydroxy-l-propyl triflate, 219, which is readily available from the diol and triflic anhydride. Oxetane 221 can also be prepared in 74% yield by treatment of the trifurazanyl ether 220 with DBU. Polymerization and copolymerization reactions of oxetane 220 have also been investigated (97MI7) (Scheme 148). 

Grignard reagents react with oxetane, a four-membered cyclic ether, to yield primary alcohols, but the reaction is much slower than the corresponding reaction with ethylene oxide. Suggest a reason for the difference in reactivity between oxetane and ethylene oxide. 

Osmium tetroxide, reaction with alkenes, 235-236 toxicity of, 235 Oxalic add, structure of, 753 Oxaloacetic acid, structure of, 753 Oxetane, reaction with Grignard reagents, 680 Oxidation, 233, 348 alcohols, 623-626 aldehydes, 700-701 aldoses, 992-994 alkenes, 233-236 biological, 625-626 phenols, 631 sulfides, 670 thiols, 668... 

By reaction with the appropropriate aryl halides can be prepared a variety of aryltin compounds that are not accessible from the reactions involving arylmagnesium halides and organotin halides (88,89) there is evidence that an aryne intermediate may be involved (90). However, for some purposes, such as the addition to carbonyl compounds, ox-iranes, and oxetanes, to give hydroxyalkyltin compounds, the Sn-Mg reagents may have advantages (see Section II,E) (91-93). 

The photoinduced [2 + 2] cycloaddition of carbonyl acceptors with electron-rich olefins leads to oxetanes (Paterno-Biichi reaction) with high regio- and stereoselectivities (equation 25). 

Other chiral oxetanes used to generate chiral y-oxido functionalized organolithium intermediates are 306-309, which gave the expected enantiopure products by reaction with non-prochiral electrophiles"" °. In all cases, when prochiral electrophilic reagents were used, a mixture of the corresponding diastereomers was obtained in variable proportions depending on the electrophile, which could be easily separated by column chromatography. 

If the olefin bears easily abstractable hydrogens, this reaction can also compete with oxetane formation and the resulting radical coupling products will predominate. This competition can be expressed as a ratio of yields of addition products to abstraction products (A add/A abs), and will be different for each pair of reactants. This ratio is delicately balanced, and seemingly small changes in the structure of either starting material can shift the predominant reaction. 

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