On the Synthesis and Reactivity of Enantiopure Azetidines

Abstract

Keywords: Azetidines / Bromocyclization / Amino alcohols / Vinylsilane / Vinyl bromide / Cyclization β-Amino alcohols with an (E)-vinylsilane moiety were cyclized in the presence of N-bromosuccinimide to afford diastereomerically pure azetidines. The chemo-and stereoselectivities of this bromocyclization are discussed. AM1 calcula-

Removal of the Pyridine Directing Group from α-Substituted N-(Pyridin-2-yl)piperidines Obtained via Directed Ru-Catalyzed sp3 C–H Functionalization

“…At room temperature, the majority of the starting material 1b remained and a mixture of the desired compound 4 and the C 2 –N benzylic-cleaved compound 5 was obtained (entry 3). As it is documented that Pd has the tendency to induce hydrogenolysis at benzylic positions, we reasoned that the formation of side product 5 might be prevented by using another transition metal to catalyze the hydrogenation. Because Pt is used for the reduction of pyridines without affecting benzylic positions, we attempted the hydrogenation step in the presence of catalytic amounts of PtO 2 , unfortunately without a positive outcome (entry 4).…”

Novel Syntheses of Azetidines and Azetidinones

“…Optically pure β-amino alcohols or methyl ethers 78 , containing a homoallylvinylsilane moiety, treated with N -bromosuccinimide (NBS), provide fair-to-good yields of azetidines 79 (Scheme ) in a totally regio- and diastereoselective manner …”

The first example of ring expansion of N-tosylaziridines to 2-aroyl-N-tosylazetidines with nitrogen ylides in an aqueous medium

“…7 Recently, 2-substituted-N-tosylazetidines have been utilized as masked 1,4-dipoles for the construction of nitrogen-containing sixmembered heterocycles. 8 Different approaches reported for the synthesis of azetidines can be broadly categorized as follows: (I) cyclizations involving C-N bond formation which include (i) intramolecular cyclizations by nucleophilic displacement of halides, sulfonic esters, triflates and epoxides by a nitrogen nucleophile, 9,10 (ii) intramolecular ring opening of bromonium, iodonium and seleniranium intermediates containing allylic and homoallylic amine systems, 11 (iii) reaction of iminium cation with allyl-and propargyltrimethylsilanes, 12 (iv) intramolecular NH insertion of diazo compounds, 13 and cyclizations of b-aminoallenes; 14 (II) cyclizations involving C-C bond formation which include (i) intramolecular nucleophilic displacement of halides by carbanion, 15 (ii) electroreductive intramolecular cross-coupling of imines bearing alkoxycarbonyl compounds and photochemically induced intramolecular cyclization of appropriate aminoketones, 16 (iii) cycloadditions, 17 (iv) ring rearrangements, 18 (v) reduction of azetidin-2-ones. 19 Very recently, an excellent review by Brandi and co-workers covered the synthesis of azetidines.…”