Chemoselective Lactam Formation in the Addition of Benzenesulfonyl Bromide to N-Allyl Acrylamides and N-Allyl 3,3-Dimethylacrylamides

Photoredox-Catalyzed Synthesis of 3-Sulfonylated Pyrrolin-2-ones via a Regioselective Tandem Sulfonylation Cyclization of 1,5-Dienes

A mild, visible-light-induced, regioselective cascade sulfonylation-cyclization of 1,5-dienes with sulfonyl chlorides through the intermolecular radical addition/cyclization of alkenes C(sp²)-H was developed. This procedure proceeds well and affords a mild and efficient route to a range of monosulfonylated pyrrolin-2-ones at room temperatures.

α,γ-Dioxygenated amides via tandem Brook rearrangement/radical oxygenation reactions and their application to syntheses of γ-lactams

Pyrrolidones are common heterocyclic fragments in various biologically active compounds. Here, a two-step radical-based approach to γ-lactams bearing three to four stereocenters starting from epoxides, N-allylic silylacetamides and TEMPO is reported. The sequence starts with a new tandem nucleophilic substitution/Brook rearrangement/single electron transfer-induced radical oxygenation furnishing orthogonally protected α,γ-dioxygenated N-allylamides with wide scope, mostly good yields, and partly good diastereo- and enantioselectivity for defined combinations of chiral epoxides and chiral amides. This represents a very rare example of an oxidative geminal C-C/C-O difunctionalization next to carbonyl groups. The resulting dioxygenated allylic amides are subsequently subjected to persistent radical effect-based 5-exo-trig radical cyclization reactions providing functionalized pyrrolidones in high yields as diastereomeric mixtures. They converge to 3,4-trans-γ-lactams by base-mediated equilibration, which can be easily further diversified. Stereochemical models for both reaction types were developed.

Regioselective, copper(i)-catalyzed, tandem sulfonylation-cyclization of 1,5-dienes with sulfonyl chlorides

A copper(i)-catalyzed sulfonylation-cyclization of 1,5-dienes with sulfonyl chlorides was developed.

Photochemical benzylic bromination in continuous flow using BrCCl3 and its application to telescoped p-methoxybenzyl protection

Photochemical benzylic bromination in flow using BrCCl₃, which is compatible with electron-rich aromatics, allowing in situ p-methoxybenzyl bromide formation and PMB-protection.

Stereospecific cyclization reaction of alkenyl esters and amides of ethenetricarboxylate

The stereospecificity of the cyclization reaction of (E)- and (Z)-2-alkenyl esters and amides of ethenetricarboxylate has been examined. The reaction of (E)/(Z)-2-butenyl esters with AlCl3 or FeCl3 gave trans-substituted chlorinated γ-lactone diastereomers stereospecifically. (E)/(Z)-2-butenyl and pentenyl amides undergo an intramolecular ene reaction at room temperature gradually. At 80 °C, the (Z)-alkenyl amides were transformed to cis-substituted ene adducts and the (E)-amides were transformed to cis- and trans-substituted ene adduct mixtures. The reaction of (E)/(Z)-2-alkenyl amides with ZnI2 gave trans-substituted γ-lactam diastereomers stereospecifically along with the ene adducts.

Kinetic studies on the formation of sulfonyl radicals and their addition to carbon-carbon multiple bonds

The reactions of α-hydroxyl and α-alkoxyl alkyl radicals with methanesulfonyl chloride (MeSO(2)Cl) have been studied by pulse radiolysis at room temperature. The alkyl radicals were produced by ionizing radiation of N(2)O-saturated aqueous solution containing methanol, ethanol, isopropanol, or tetrahydrofuran. The transient optical absorption spectrum consisted of a broad band in the region 280-380 nm with a maximum at 320 nm typical of the MeSO(2)(•) radical. The rate constants in the interval of 1.7 × 10(7)-2.2 × 10(8) M(-1) s(-1) were assigned to an electron-transfer process that leads to MeSO(2)Cl(•-), subsequently decaying into MeSO(2)(•) radical and Cl(-). The rate constants for the addition of CH(3)SO(2)(•) to acrolein and propiolic acid were found to be 4.9 × 10(9) M(-1) s(-1) and 5.9 × 10(7) M(-1) s(-1), respectively, in aqueous solutions and reversible. The reactivity of tosyl radical (p-CH(3)C(6)H(4)SO(2)(•)) toward a series of alkenes bearing various functional groups was also determined by competition kinetics in benzene. The rate constants for the addition of tosyl radical to alkenes vary in a much narrower range than the rate constants for the reverse reaction. The stabilization of the adduct radical substantially contributes to the increase of the rate constant for the addition of tosyl radical to alkenes and, conversely, retards the β-elimination of tosyl radical.

Synthesis of fused piperidinones through a radical-ionic cascade

Azabicyclo[4.3.0]nonanes were assembled, from chiral allylsilanes possessing an oxime moiety, using a stereocontrolled formal [2 + 2 + 2] radical-ionic process. The cascade involves the addition of an alpha-iodoester to the less substituted end of the enoxime which is then followed by a 5-exo-trig cyclization onto the aldoxime function, producing an alkoxyaminyl radical species which finally lactamizes to afford the titled piperidinone. High levels of stereoinduction were observed, demonstrating the ability of a silicon group located at the allylic position to efficiently control the stereochemistry of the two newly created stereogenic centers. When the radical cascade was extended to ketoximes, the resulting sterically hindered alkoxyaminyl radical did not react further with the initiator Et3B to produce the expected nucleophilic amidoborane complex. In sharp contrast, this long-lived radical recombined with the initial alpha-stabilized ester radical to produce a cyclopentane incorporating two ester fragments.

Chameleon Reactivity of the Allene Bond of 4-Vinylidene-2-oxazolidinone: Novel Through-Space Conjugative Nucleophilic Addition of Electron-Rich Alkenes and Hetero-Nucleophiles

The Calpha==Cbeta double bond of allene carbamates 1 serves as an electron acceptor similar to the double bond of conjugated enones by means of a through-space interaction with the N--SO2 bond; the carbamate double bond is thus subject to nucleophilic addition for a wide variety of nucleophiles, which proceeds under mild conditions by heating at 70-100 degrees C. Depending on the kind of nucleophiles, 1 displays three different reaction modes: 1) Typically enol ethers and allylsilanes promote 1,3-sulfonyl migration of 1 and undergo the inverse electron demand Diels-Alder reaction with the 1-aza-1,3-butadiene intermediates II thus formed to furnish bicyclic 2-alkoxy-5-sulfonyltetrahydropyridines 2 and 2-silylmethyl-5-sulfonyltetrahydropyridines 3, respectively, with high regio- and stereoselectivity and retention of configuration of the double bonds of these electron-rich alkenes; 2) silanes (RnSiH4-n, n=1-3) and thiols deliver the hydride and the thiolate at the Cbeta carbon and promote the 1,3-sulfonyl migration, followed by protonation of the thus-formed carbamate anion (Z)-III to provide, for example, (Z)-4 a and (Z)-4 j, respectively; 3) alcohols simply add to the Calpha==Cbeta double bond and provide (E)-6. Usually, the reaction with alcohols is accompanied by the second pathway, giving rise to, for example, (Z)-4 b in addition to (E)-6 b. Phenol engages in the third pathway and provides (E)-6 g exclusively. Heteroaromatics, such as furans and benzofurans follow the first pathway, however, in a different regioselectivity from enol ethers and allylsilanes, delivering the oxygen atom at the 3-position of 5-sulfonyltetrahydropyridines (2 g and 2 h). Indoles, on the other hand, show a dichotomy, equally enjoying the first and the third pathways and provide mixtures of (E)-7 and (E)-8, respectively.

Synthesis of functional aromatic multisulfonyl chlorides and their masked precursors

The synthesis of functional aromatic bis(sulfonyl chlorides) containing an acetophenone and two sulfonyl chloride groups, i.e., 3,5-bis[4-(chlorosulfonyl)phenyl]-1-acetophenone (16), 3,5-bis(chlorosulfonyl)-1-acetophenone (17), and 3,5-bis(4-(chlorosulfonyl)phenyloxy)-1-acetophenone (18) via a sequence of reactions, involving in the last step the quantitative oxidative chlorination of S-(aryl)- N,N'-diethylthiocarbamate, alkyl- or benzyl thiophenyl groups as masked nonreactive precursors to sulfonyl chlorides is described. A related sequence of reactions was used for the synthesis of the aromatic trisulfonyl chloride 1,1,1-tris(4-chlorosulfonylphenyl)ethane (24). 4-(Chlorosulfonyl)phenoxyacetic acid, 2,2-bis[[[4-(chlorosulfonyl)phenoxyacetyl]oxy]methyl]-1,3-propanediyl ester (27), 5,11,17,23-tetrakis(chlorosulfonyl)-25,26,27,28-tetrakis(ethoxycarbonylmethoxy)calix[4]arene (38), 5,11,17,23,29,35-hexakis(chlorosulfonyl)-37,38,39,40,41,42-hexakis(ethoxycarbonylmethoxy)calix[6]arene (39), 5,11,17,23,29,35,41,47-octakis(chlorosulfonyl)-49,50,51,52,53,54,55,56-octakis(ethoxycarbonylmethoxy)calix[8]arene (40), 5,11,17,23-tetrakis(tert-butyl)-25,26,27,28-tetrakis(chlorosulfonyl phenoxyacetoxy)calix[4]arene (44), 5,11,17,23,29,35-hexakis(tert-butyl)-37,38,39,40,41,42-hexakis(chlorosulfonylphenoxyacetoxy)calix[6]arene (45), and 5,11,17,23,29,35,41,47-octakis(tert-butyl)-49,40,51,52,53,54,55,56-octakis(chlorosulfonylphenoxyacetoxy)calix[8]arene (46) were synthesized by two different multistep reaction procedures, the last step of both methods consisting of the chlorosulfonation of compounds containing suitable activated aromatic positions. 2,4,6-Tris(chlorosulfonyl)aniline (47) was obtained by the chlorosulfonation of aniline. The conformation of two series of multisulfonyl chlorides i.e., 38, 39, 40 and 44, 45, 46, was investigated by (1)H NMR spectroscopy. The masked nonreactive precursor states of the functional aromatic multisulfonyl chlorides and the aromatic multisulfonyl chlorides reported here represent the main starting building blocks required in a new synthetic strategy elaborated for the preparation of dendritic and other complex organic molecules.