Cobalt-Catalyzed Regio- and Stereoselective Hydroboration of Allenes

An efficient pincer-ligand-based cobalt-complex-catalyzed allene hydroboration affording Z-allylic boronates is described. The reaction demonstrates an excellent regio- as well as Z-stereoselectivity and a wide substrate scope that tolerates many functional groups. Based on solvent-assisted electrospray ionization mass spectrometry (SAESI-MS) studies, a rationale for the cobalt-catalyzed hydroboration involving the highly selective insertion of an allene into the Co−H bond to form Z-allylic cobalt intermediates is proposed.     

Rhodium‐Catalyzed Parallel Kinetic Resolution of Racemic Internal Allenes Towards Enantiopure Allylic 1,3‐Diketones

A rare case of a parallel kinetic resolution of racemic 1,3‐disubstituted allenes by means of a rhodium‐catalyzed addition to 1,3‐diketones furnishing enantiopure allylic 1,3‐diketones is described. Mechanistic experiments demonstrate that the different allene enantiomers react in parallel to either the diastereomeric E‐ or Z‐allylic 1,3‐diketones with the same absolute configuration of the newly formed stereogenic center. A broad substrate scope demonstrates the synthetic utility of this new method.     

Reprint of: Recent advances in the functionalization of allenes via radical process

This review is focused on the recent advances in the functionalization of allenes via radical process. Different radical partners including carbon radicals and heteroatom radicals are discussed in the reactions of allenes. Generally, the radical formed in situ would attack the allene at the central carbon leading to allyl radical intermediate. However, the formation of alkenyl radical intermediate from allene could be observed as well in some cases with high regioselectivity and stereoselectivity.     

Asymmetric Wacker-Type Oxyallenylation and Azaallenylation of Cyclic Alkenes

Palladium-catalyzed three-component carboetherification of cyclic alkenes proceeded to give trans adducts exclusively with excellent enantioselectivity through a Wacker-type pathway. The reaction is also applicable to other oxygen nucleophiles, such as water, phenols, and carboxylic acids, as well as some electron-poor aryl amines.     

2,2-Dimethylpenta-3,4-dienal derivatives: Preparation,NMR spectra,and crystal structure

Summary The preparation of some new 2,2-dimethylpenta-3,4-dienal derivatives starting byClaisen-Cope rearrangement of the pyrolytic product of the corresponding acetales and followed by condensation reactions is described. The synthesis of homoallenylketone5 from homoallenylaldehyde3 byGrignard reaction and followed by the oxidation of the formed alcohol using potassium chlorochromate (KCC) is reported. All new compounds are characterized by IR, MS,¹H, and¹³C NMR spectroscopy. The full assignment of the NMR signals is based on HETCOR and FLOCK pulse sequences. The molecular and crystal structure of 2,2-dimethylhexa-3,4-dienal 2,4-dinitrophenylhydrazone is presented.Dedicated to ProfessorFritz Sauter on the occasion of his 65th birthday