Highly Functionalised Cyclobutanols by Samarium(II) Iodide Induced Radical Cyclisations of Carbohydrate‐Derived Unsaturated Ketones

Abstract

Certain carbohydrates have been found to be excellent precursors for the samarium diiodide‐mediated 4‐exo‐trig cyclisation reaction of their keto‐olefin derivatives, which were readily prepared in a few easy steps. The cyclisation was found to be stereoselective, affording cis products, the diastereoselective excesses of which were influenced by the nature of the protecting group employed at C5−O of the furanose sugar. The major chiral cyclobutane product of the cyclisation step was converted into an advanced intermediate for the synthesis of a nucleoside anti‐viral analogue. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Cross-Coupling Reactions Using Samarium(II) Iodide

“…179 The Williams group has also reported the cross-coupling of ketones with α,β-unsaturated esters mediated by SmI 2 to produce cyclobutanols (Scheme 9). 180,181 Carbohydrate-derived unsaturated ketones underwent efficient 4-exo-trig cyclization using the SmI 2 −HMPA system. 180 (Z)-and (E)-olefin isomers provided access to complementary diastereoisomers of the cyclobutanol products.…”

“…180,181 Carbohydrate-derived unsaturated ketones underwent efficient 4-exo-trig cyclization using the SmI 2 −HMPA system. 180 (Z)-and (E)-olefin isomers provided access to complementary diastereoisomers of the cyclobutanol products. In some cases, the order of addition (substrate to SmI 2 −HMPA) was found to be critical to avoid formation of cyclopentane dimers, arising from anionic ment of unsaturated ketones 31 with SmI 2 −MeOH resulted in the spirocyclization to yield cyclopentanol products in modest yields due to the steric hindrance at the α-position of the ketone moiety; however, a substrate containing a protected hydroxyl methyl group allowed access to the desired product in high yield.…”

Titanocene Catalyzed 4-exo Cyclizations: Mechanism, Experiment, Catalyst Design

“…Progress toward efficient 4- exo cyclizations has thus been more successful. With SmI 2 , the currently most popular electron-transfer reagent, cyclizations with ketyl radicals and acrylates or vinylsulphones as radical traps result in the formation of cyclobutanols . However, the use of ketones as radical precursors may lead to undesired 5- endo cyclizations 8c…”

Synthesis of 4-Membered Carbasugars by Way of Stereoselective SmI2-Mediated Aldehyde–Alkene Cyclization

“…Our retrosynthetic analysis takes advantage of the chirality of 1 , which provides two stereogenic centers (C1 and C2) of the final compounds and secures the stereocontrol of the key reductive coupling reaction from γ,δ-unsaturated aldehydes III (Scheme ). This pivotal step based on an intramolecular SmI 2 -mediated carbonyl–alkene coupling was expected to provide cyclobutanols II with the four contiguous stereogenic centers of the target molecules of type I with predictable stereocontrol. The absolute configuration of the resulting alcohol at C3 may be directly inverted to provide access to further members of carbaoxetanoses of type I ′.…”