Generation and alkylation reaction of 1-bromoalkenylzincate

Stereospecific alkenylidene homologation of organoboronates by SNV reaction

Concerted nucleophilic substitution, known as SN2 reaction, is a fundamental organic transformation used in synthesis to introduce new functional groups and construct carbon-carbon and carbon-heteroatom bonds1. SN2 reactions typically involve backside attack of a nucleophile to the σ* orbital of a C(sp3)-X bond (X = halogen or other leaving group), resulting in complete inversion of a stereocentre2. By contrast, the corresponding stereoinvertive nucleophilic substitution on electronically unbiased sp2 vinyl electrophiles, namely concerted SNV(σ) reaction, is much rarer, and so far limited to carefully designed substrates mostly in ring-forming processes3,4. Here we show that concerted SNV reactions can be accelerated by a proposed strain-release mechanism in metallated complexes, leading to the development of a general and stereospecific alkenylidene homologation of diverse organoboronates. This method enables the iterative incorporation of multiple alkenylidene units, giving cross-conjugated polyenes that are challenging to prepare otherwise. Further application to the synthesis of bioactive compounds containing multi-substituted alkenes is also demonstrated. Computational studies suggest an unusual SN2-like concerted pathway promoted by diminishing steric strain in the square planar transition state, which explains the high efficiency and stereoinversive feature of this metallate SNV reaction.

Recent Advances of the Halogen-Zinc Exchange Reaction

For the preparation of zinc organometallics bearing highly sensitive functional groups such as ketones, aldehydes or nitro groups, especially mild halogen-zinc exchange reagents have proven to be of great potential. In this Minireview, the latest research in the area of the halogen-zinc exchange reaction is reported, with a special focus lying on novel dialkylzinc reagents complexed with lithium alkoxides. Additionally, the preparation and application of organofluorine zinc reagents and transition-metal-catalyzed halogen-zinc exchange reactions are reviewed.

Type-I dyotropic rearrangement for 1,2-disubstituted cyclohexanes: substitution effect on activation energy

Migratory aptitude and contribution of specific structural features of synthetically valuable functional groups and halogen atoms in type-I dyotropic rearrangement for both symmetric and unsymmetrical 1,2-disubstituted cyclohexanes are computed.

Polyborylated reagents for modern organic synthesis

Diverse kinds of gem- and vic-diborylated compounds are now readily available thanks to advances in gem-diborylation of lithium carbenoids as well as vic-diborylation of carbon-carbon multiple bonds with diboron compounds. These diborylated reagents lead to invention of polyborylated reagents and many novel and useful synthetic methods for supreme stereocontrol. This review summarizes preparative methods and synthetic reactions of di- and polyborylated reagents with the emphasis on multiple bond formation.

Deprotonative Metalation Using Ate Compounds: Synergy, Synthesis, and Structure Building

Historically, single-metal organometallic species such as organolithium compounds have been the reagents of choice in synthetic organic chemistry for performing deprotonation reactions. Over the past few years, a complementary new class of metalating agents has started to emerge. Owing to a variable central metal (magnesium, zinc, or aluminum), variable ligands (both in their nature and number), and a variable second metallic center (an alkali metal such as lithium or sodium), "ate" complexes are highly versatile bases that exhibit a synergic chemistry which cannot be replicated by the homometallic magnesium, zinc, or aluminum compounds on their own. Deprotonation accomplished by using these organometallic ate complexes has opened up new perspectives in organic chemistry with unprecedented reactivities and sometimes unusual and unpredictable regioselectivities.

A convenient preparation of xanthene dyes

A facile synthetic route utilizing readily available reagents affords a series of regioisomerically pure xanthene dye derivatives. Advantages include relatively mild conditions and good to excellent yields. Nonpolar, highly crystalline intermediates are isolable by standard chromatographic techniques. The intermediates are in the requisite xanthene oxidation state, thus avoiding the need for relatively inefficient oxidation chemistry and/or harsh conditions. During the course of this work, a new boron-mediated 1,2-aryl migration reaction was discovered.

Reactions of gem-dibromo compounds with trialkylmagnesate reagents to yield alkylated organomagnesium compounds

The reaction of gem-dibromocyclopropanes 5 with nBu(3)MgLi affords butylated cyclopropylmagnesium species that can be trapped with various electrophiles. The reaction of dibromomethylsilanes 12 requires the addition of a catalytic amount of CuCN small middle dot2 LiCl for smooth migration of the alkyl groups. The resultant alpha-silylpentylmagnesium compounds 16 react with electrophiles, such as acyl chlorides or alpha,beta-unsaturated ketones to afford alpha- or gamma-silyl ketones, respectively. Treatment of dibromodisilylmethanes with Me(3)MgLi yields 1-bromo-1,1-disilylethanes 25 that can be converted into 1,1-disilylethenes 29 by dehydrobromination.

Oxygen capture by lithiated organozinc reagents containing aromatic 2-pyridylamide ligands

The sequential reaction of ZnMe2 with a 2-pyridylamine (HN(2-C5H4N)R, R = Ph: 1; 3,5-Xy (=3,5-xylyl): 2; 2,6-Xy: 3; Bz (=benzyl): 4; Me: 5), tBuLi and thereafter with oxygen affords various lithium zincate species, the solid-state structures of which reveal a diversity of oxo-capture modes. Amine 1 reacts to give both dimeric THF [Li(Me)OZn[N(2-C5H4N)Ph]2] (6), wherein oxygen has inserted into the Zn-C bond of a [MeZn[N(2-C5H4N)-Ph]2] ion, and the trigonal Li2Zn complex, bis(OtBu)-capped (THF x Li)2-[[(mu3-O)tBu]2Zn[N(2-C5H4N)Ph]2] (7). The structural analogue of 6 (8) results from the employment of 2, while the use of more sterically congested 3 yields a pseudo-cubane dimer [(THF x [Li(tBu)OZn(OtBu)Me]]2] (9) notable for the retention of labile Zn-C(Me). Amines 4 and 5 afford the oxo-encapsulation products [mu4-O)Zn4[(2-C5H4N)-NBz]6] (10b), and [tBu(mu3-O)-Li3(mu6-O)Zn3[(2-C5H4N)NMe]6] (11), respectively, with concomitant oxo-insertion into a Li-C interaction resulting in capping of the fac-isomeric (mu6-O)M3M'3 distorted octahedral core of the latter complex by a tert-butoxide group.