Highly Z-Selective Horner–Wadsworth–Emmons Olefination Using Modified Still–Gennari-Type Reagents

In this report, new, easily accessible reagents for highly Z-selective HWE reactions are presented. Alkyl di-(1,1,1,3,3,3-hexafluoroisopropyl)phosphonoacetates, structurally similar to Still–Gennari type reagents, were tested in HWE reactions with a series of various aldehydes. Very good Z-selectivity (up to a 98:2 Z:E ratio) was achieved in most cases along with high yields. Application of the new reagents may be a valuable, practical alternative to the well-established Still–Gennari or Ando Z-selective carbonyl group olefination protocols.     

A 2,6‐Bis(phenylamino)pyridinato Titanium Catalyst for the Highly Regioselective Hydroaminoalkylation of Styrenes and 1,3‐Butadienes

The C? C bond forming catalytic hydroaminoalkylation of terminal alkenes, 1,3‐dienes, or styrenes allows a direct and highly atom efficient (100 %) synthesis of amines which can result in the formation of two regioisomers, the linear and the branched product. We present a new titanium catalyst with 2,6‐bis(phenylamino)pyridinato ligands for intermolecular hydroaminoalkylation reactions of styrenes and 1‐phenyl‐1,3‐butadienes that delivers the corresponding linear hydroaminoalkylation products with excellent regioselectivities.     

Divergent Synthesis of CF3‐Substituted Allenyl Nitriles by Ligand‐Controlled Radical 1,2‐ and 1,4‐Addition to 1,3‐Enynes

A ligand‐controlled system that enables regioselective trifluoromethylcyanation of 1,3‐enynes has been identified, which provides access to a variety of CF₃‐containing tri‐ and tetrasubstituted allenyl nitriles. We disclose that the involved propargylic radicals can be selectively trapped by (Box)Cu^II cyanide, while the tautomerized allenyl radicals are trapped by (phen)Cu^II cyanide (Box= bisoxazoline, phen=phenanthroline). In addition, the reaction features broad substrate scope and excellent functional group compatibility. Moreover, this protocol represents a novel regioselectivity‐tunable functionalization of 1,3‐enynes via radicals, which we believe will have great implications for the development of catalytic systems for selectivity control in radical and organometallic chemistry.     

Stereoselective Synthesis of Highly Substituted Conjugated Dienes via Pd‐Catalyzed Carbonylation of 1,3‐Diynes

The stereoselective synthesis of conjugated dienes was realized for the first time via Pd‐catalyzed alkoxycarbonylation of easily available 1,3‐diynes. Key to success is the utilization of the specific ligand 1,1′‐ferrocenediyl‐bis(tert‐butyl(pyridin‐2‐yl)phosphine) ( L1 ), which allows this novel transformation to proceed at room temperature. A range of 1,2,3,4‐tetrasubstituted conjugated dienes are obtained in this straightforward access in high yields and selectivities. The synthetic utility of the protocol is showcased in the concise synthesis of several important intermediates for construction of natural products rac‐cagayanin, rac‐galbulin, rac‐agastinol, and cannabisin G.     

Asymmetric Copper‐Catalyzed Vinylogous Mukaiyama Michael Addition of Cyclic Dienol Silanes to Unsaturated α‐Keto Phosphonates

A highly stereoselective vinylogous Mukaiyama Michael reaction (VMMR) leading to α‐keto phosphonate‐containing γ‐butenolides with two stereogenic centers is described. The presented transformation is catalyzed by a combination of a commercially available C₂‐symmetric bisoxazoline (BOX) ligand and a copper salt and tolerates a variety of nucleophiles and electrophiles. The stereoselectivities of the reactions are good to excellent and the products are obtained in moderate to high yields.     

Synthesis and Properties of 2,3‐Diethynyl‐1,3‐Butadienes

The first general preparative access to compounds of the 2,3‐diethynyl‐1,3‐butadiene (DEBD) class is reported. The synthesis involves a one‐pot, twofold Sonogashira‐type, Pd⁰‐catalyzed coupling of two terminal alkynes and a carbonate derivative of a 2‐butyne‐1,4‐diol. The synthesis is broad in scope and members of this structural family are kinetically stable enough to be handled using standard laboratory techniques at ambient temperature. They decompose primarily through heat‐promoted cyclodimerizations, which are impeded by alkyl substitution and accelerated by aryl or alkenyl substitution. An iterative sequence of these unprecedented Sonogashira‐type couplings generates a new type of expanded dendralene. A suitably substituted DEBD carrying two terminal alkyne groups undergoes Glaser–Eglinton cyclo‐oligomerization to produce a new class of expanded radialenes, which are chiral due to restricted rotation about their 1,3‐butadiene units. The structural features giving rise to atropisomerism in these compounds are distinct from those reported previously.     

Carbohydrate‐2‐deoxy‐2‐phosphonates: Simple Synthesis and Horner–Emmons Reaction

Phosphorus meets carbohydrates : Dimethyl phosphite reacts with ceric(IV) ammonium nitrate (CAN) to give phosphonyl radicals that add to glycals 1 . The derivatives 2 were isolated in high yields and during a subsequent Horner–Emmons reaction underwent an interesting elimination to give 3,6‐dihydro‐2H‐pyrans 3 . The short sequence with simple precursors is applicable to the transformation of hexoses, pentoses, and disaccharides. Bn=benzyl.

     

Diethylbis(2,2′‐bipyridine)iron/MAO. A Very Active and Stereospecific Catalyst for 1,3‐Diene Polymerization

Diethylbis(2,2′‐bipyridine)Fe/MAO is an extremely active catalyst for the polymerization of 1,3‐dienes. Polymers with a 1,2 or 3,4 structure are formed from butadiene, isoprene, (E)‐1,3‐pentadiene and 3‐methyl‐1,3‐pentadiene, while cis‐1,4 polymers are derived from 2,3‐dimethyl‐1,3‐butadiene. The 1,2 (3,4) polymers obtained at 25°C are amorphous, while those obtained below 0°C are crystalline, as was determined by means of X‐ray diffraction. Mechanistic implications of the results are briefly discussed.