Stereoselectivity of 6-ExoCyclization of α-Carbamoyl Radicals

Abstract

The stereoselectivity in the 6-exo cyclization of α-carbamoyl radicals was investigated experimentally and theoretically. The BEt3/O2-initiated iodine-atom-transfer radical cyclization reactions of substituted N-(but-3-en-1-yl)-N-(tert-butyl)-2-iodoalkanamides were carried out, which led to the predominant formations of 3,4-cis, 4,5-trans, or 4,6-trans substituted δ-lactams. Density functional calculations at the B3LYP/6-31G* level revealed that the 6-exo radical cyclization proceeds via boat-conformational transition states. Furthermore, a mechanistic insight into the stereoselectivity was provided and the calculation results were in excellent agreement with the experimental observations.

Photoredox catalysis in the synthesis of γ- and δ-lactams from N-alkenyl trichloro- and dichloroacetamides

“…In addition, butenyl derivative 1l gave exclusively the expected 6- exo cyclization product 2l with very good yields including when water was used as a solvent (entry 4). 17…”

Ammonium Persulfate Promotes Radical Cyclization of 1,3‐Dicarbonyl‐Ugi 4‐CR Adducts: Synthesis of Polysubstituted γ‐Lactams in Aqueous Media

“…Intrigued by the possibility of accessing a nitrogen‐based six‐membered ring 26 (δ‐valerolactam) by using this radical protocol, an Ugi adduct model 25 was synthesized from 4‐pentenoic acid 24 and tested in the cyclization (62 % yield). Unfortunately, the radical process did not operate under the developed conditions, observing decomposition events in the adduct, may be attributed to the relative slow radical cyclization rate of the 6‐ exo‐trig process respect to the 5‐ exo mode (Scheme ) …”

Asymmetric Synthesis of Six-Membered Cyclic Sulfamides via Palladium-Catalyzed Alkene Carboamination Reactions

“…General procedure 2 was employed for the sulfonylation of N-(tertbutyl)but-3-en-1-amine 15 (1.34 g, 10.5 mmol) with 3-(N-benzylsulfonyl)oxazolidin-2-one (2.43 g, 9.5 mmol). This procedure afforded the title compound (670 mg, 24%) as a colorless solid; mp 44-47 °C.…”