IPy2BF4-Mediated Rearrangements of 1,2-Difunctionalized Compounds and Olefins

Recent progress of 1,1-difunctionalization of olefins

Olefins are a very important class of compounds and broadly used in the construction of various synthetic building blocks and practical industrial production. The difunctionalization of olefins provides one of the most powerful methods for the C-C or C-X bond formation with a rapid increase of the molecular complexity and synthetic value economically and effectively. Compared with the vigorous growth and abundant achievements of 1,2-difunctionalization of olefins, 1,1-difunctionalization is a relatively emerging and inadequately exploited research direction, despite being tremendously attractive from synthetic perspectives. In this minireview, we provide a brief overview of the advancements of 1,1-difunctionalization of olefins in the past twenty years, and prospects of future developments.

Iodine-Mediated Oxidative Rearrangement of α,β-Unsaturated Diaryl Ketones: A Facile Access to 1,2-Diaryl Diketones

A metal-free oxidative rearrangement was explored for the synthesis of 1,2-diaryl diketones by utilizing α,β-unsaturated diaryl ketones and I2/TBHP in good to high yields. The reaction proceeds via oxidative aryl migration, followed by C-C bond cleavage. A simple and high-yielding protocol was developed for the synthesis of a wide range of 1,2-diaryl diketones, which are the backbone for a variety of medicinally important molecules.

Selone-stabilized aryltellurenyl cations

Controlled bromination of a diarylditelluride, R2Te2 (R = 2,6-dimethylphenyl) (6) in dichloromethane led to the formation of a Te(II)-Te(IV) mixed-valent tellurenyl bromide, RBr2TeTeR (7). A further reaction of 7 with 1,3-dibutylbenzimidazolin-2-selone, C15H22N2Se (L) (9), produced the first selone adduct of the 2,6-dimethylphenyltellurenyl cation with the 2,6-dimethylphenyltellurium dibromide anion, [(2,6-Me2C6H3)Te(L)](+)[(2,6-Me2C6H3)TeBr2](-) (10). The red colored cationic adduct 10 is not stable in acetonitrile and disproportionated to give the selone adduct of 2,6-dimethylphenyltellurenyl bromide, [(2,6-Me2C6H3)Te(L)Br] (11b) and bis(2,6-dimethylphenyl)tellurium dibromide, [(2,6-Me2C6H3)2TeBr2], (13). The metathesis reaction of 11b with AgBF4 produced a stable dark red colored selone adduct of the 2,6-dimethylphenyltellurenyl cation with the BF4(-) anion, [(2,6-Me2C6H3)Te(L)](+)BF4(-) (15). The selone adducts of aryltellurenyl halides, i.e. [(2,6-Me2C6H3)Te(L)X] (X = Cl, Br, I) (11a-11c), have been synthesized by a one-pot reaction of 6 with an equimolar mixture of 9 and 1,3-dibutylbenzimidazolin-2-dihaloselones, C15H22N2SeX2 (14a-14c). Triphenylphosphine (PPh3), when treated with [(2,6-Me2C6H3)Te(L)X] (11a-11c), substitutes selone from the adduct to afford the triphenylphosphine adducts of aryltellurenyl halides, [(2,6-Me2C6H3)Te(PPh3)X] (16a-16c).

Reactive p-block cations stabilized by weakly coordinating anions

The chemistry of the p-block elements is a huge playground for fundamental and applied work. With their bonding from electron deficient to hypercoordinate and formally hypervalent, the p-block elements represent an area to find terra incognita. Often, the formation of cations that contain p-block elements as central ingredient is desired, for example to make a compound more Lewis acidic for an application or simply to prove an idea. This review has collected the reactive p-block cations (rPBC) with a comprehensive focus on those that have been published since the year 2000, but including the milestones and key citations of earlier work. We include an overview on the weakly coordinating anions (WCAs) used to stabilize the rPBC and give an overview to WCA selection, ionization strategies for rPBC-formation and finally list the rPBC ordered in their respective group from 13 to 18. However, typical, often more organic ion classes that constitute for example ionic liquids (imidazolium, ammonium, etc.) were omitted, as were those that do not fulfill the - naturally subjective -"reactive"-criterion of the rPBC. As a rule, we only included rPBC with crystal structure and only rarely refer to important cations published without crystal structure. This collection is intended for those who are simply interested what has been done or what is possible, as well as those who seek advice on preparative issues, up to people having a certain application in mind, where the knowledge on the existence of a rPBC that might play a role as an intermediate or active center may be useful.

Enantioselective Oxidative Rearrangements with Chiral Hypervalent Iodine Reagents

A stereoselective hypervalent iodine‐promoted oxidative rearrangement of 1,1‐disubstituted alkenes has been developed. This practically simple protocol provides access to enantioenriched α‐arylated ketones without the use of transition metals from readily accessible alkenes.

Hypoiodous acid-catalyzed regioselective geminal addition of methanol to vinylarenes: synthesis of anti-Markovnikov methyl acetals

A new metal-free catalytic approach for the synthesis of anti-Markovnikov methyl acetals from vinylarenes based on in situ generated HOI species is reported. The mechanistic investigations provided the solid evidence for the proposed mechanism.