2.1.5. Electrophilic Attack on CdC 3994 2.1.6. NH Insertions in Diazo Compounds 3994 2.1.7. Pd Catalyzed Cyclizations 3994 2.2. Cyclizations by C-C Bond formation 3995 2.2.1. Nucleophilic Displacement of Halides 3995 2.2.2. Cyclizations Involving CdO Group 3995 2.3. Cycloadditions 3996 2.4. Ring Rearrangements 3997 2.4.1. Rearrangements of Four-Membered Rings 3997 2.4.2. Rearrangements of Larger Rings 3998 2.5. Reduction of Azetidin-2-ones 3998 2.6. Miscellaneous Syntheses 3999 2.7. Important Classes of Compounds 4000 2.7.1. Natural Products 4000 2.7.2. Azetidine Carboxylic Acids 4001 2.7.3. Exomethylene Azetidines 4002 2.7.4. Ligands for Metal-Catalyzed Reactions and Chiral Auxiliaries 4003

Novel syntheses of azetidines and azetidinones.

Cyclizations of Alkynes: Revisiting Baldwin’s Rules for Ring Closure

Gold‐Catalyzed Intramolecular Carbothiolation of Alkynes: Synthesis of 2,3‐Disubstituted Benzothiophenes from (α‐Alkoxy Alkyl) (ortho‐Alkynyl Phenyl) Sulfides

Progress in the synthesis and transformations of alkylidenecyclopropanes and alkylidenecyclobutanes.

This work reexamined the stereoelectronic basis for the “favored attack trajectories” regarding the nucleophilic and radical cyclizations of alkynes. In contrast to the original Baldwin rules, the acute attack angle of a nucleophile leading to the proposed endo-dig preference for the formation of small cycles is less favorable stereoelectronically than the alternative obtuse trajectory leading to the formation of exo-dig products. For smaller cycles, this intrinsic stereoelectronic preference can be masked by the greater thermodynamic stability of the less strained endo-products. Unbiased comparison of competing cyclization attacks has been accomplished via dissection of the activation barrier into the intrinsic barrier and thermodynamic component via Marcus theory. Intrinsic barriers of thermoneutral reactions strongly favor exo-dig closures, in full accord with the greater magnitude of two-electron bond forming interactions for the obtuse trajectory. This analysis agrees very well with experimental obse...

Rules for anionic and radical ring closure of alkynes.

Pd-catalyzed intramolecular selenocarbamoylation of alkynes leading to alpha-alkylidene-beta-lactams was developed. This reaction can be applied to thiocarbamoylation and to the synthesis of delta- and epsilon-lactams and a cyclobutanone.

Palladium-catalyzed intramolecular selenocarbamoylation of alkynes with carbamoselenoates: formation of alpha-alkylidene-beta-lactam framework.

A new entry to α-alkylidene-β-lactams by 4-exo-dig cyclization of carbamoyl radicals

Palladium-Catalyzed Intramolecular Selenocarbamoylation of Allenes with Carbamoselenoates: A New Entry to α,β-Unsaturated Lactams

A new synthetic method of α-alkylidene-β-lactam frameworks has been developed. Irradiation of carbamotelluroates 5 having a propargylic group at the nitrogen atom with visible light afforded α-telluromethylene-β-lactams 6 by 4- exo - dig cyclization of carbamoyl radicals, generated by homolytic cleavage of carbamoyl carbon–tellurium bond of 5 , with internal C–C triple bond. Density functional theory (DFT) calculations on cyclization step indicate that 4- exo - dig cyclization of carbamoyl radicals is kinetically favored. The existence of a rapid equilibrium between carbamoyl and four-membered vinyl radicals was suggested by control experiments using the corresponding carbamoselenoate.

A New Entry to α-Alkylidene-β-lactams by 4-exo-Dig Cyclization of Carbamoyl Radicals.

Pd(PPh3)4-catalyzed intramolecular selenocarbamoylation of allenes led to the regioselective formation of α,β-unsaturated five- and six-membered lactams having an allyl selenide unit. This procedure could be applied to the synthesis of the corresponding sulfur analogue by thiocarbamoylation as well as a cyclopentenone. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Masashi Toyofuku

Papers

Palladium-catalyzed intramolecular selenocarbamoylation of alkynes with carbamoselenoates: formation of alpha-alkylidene-beta-lactam framework.

A new entry to α-alkylidene-β-lactams by 4-exo-dig cyclization of carbamoyl radicals

Palladium-Catalyzed Intramolecular Selenocarbamoylation of Allenes with Carbamoselenoates: A New Entry to α,β-Unsaturated Lactams

A New Entry to α-Alkylidene-β-lactams by 4-exo-Dig Cyclization of Carbamoyl Radicals.

Palladium‐Catalyzed Intramolecular Selenocarbamoylation of Allenes with Carbamoselenoates: A New Entry to α,β‐Unsaturated Lactams.