Alkenylation of imines

Intermolecular carbon-carbon bond formation of alkenylsilanes by electrophilic substitution is rather limited except for the reaction with acyl chlorides.1. The alkenylations of imines and epoxides are achieved with electronically activated alkenylsilanes (Equation (3)).2 a Alkynylsilanes have frequently been used for intermolecular alkynylation of carbon electrophiles activated by a Lewis acid.30 30a-30d... 

Scheme 7.50 Formal alkenylation of imines with vinylogous aza-enamines.

A variety of electrophiles are employed for carbonyl alkenylation and arylation that proceed through transmetalation from silicon to transition metal catalysts. For example, addition of alkenylsilanes and aryl(trimethoxy)si lanes to aldehydes is catalyzed by copper/DTBM-SEGPHOS, which mediates transmetalation from silicon to copper to give a wide variety of chiral alcohols with high degree of % ee (Scheme 3-144). The enantioselective alkenylation of imines using 2-(hydroxylmethyl)phenyl-substituted propen-2-ylsilane is catalyzed by a rhodium/chiral diene complex. ... 

Shibasaki et al. developed a polymer-supported bifunctional catalyst (33) in which aluminum was complexed to a chiral binaphtyl derivative containing also two Lewis basic phosphine oxide-functionahties. The binaphtyl unit was attached via a non-coordinating alkenyl Hnker to the Janda Jel-polymer, a polystyrene resin containing flexible tetrahydrofuran-derived cross-Hnkers and showing better swelling properties than Merifield resins (Scheme 4.19) [105]. Catalyst (33) was employed in the enantioselective Strecker-type synthesis of imines with TMSCN. 

Aza-1,3-dienes. The reaction of imines (1) of aldehydes obtained from bis(trimethylsilyl)methylamine with aldehydes catalyzed by Bu4NF (Peterson alkenylation) provides 2-aza-l,3-dienes in 65-78% yield. 

Chiral allylation of imines by an allylstannane is promoted by a bis-Ji-allylpalladium complex based on the pinane skeleton, while using triallylborane to supply the allyl group a polymer-supported arenesulfonaminoisobomeol can provide a proper environment. The chirality of alkenyl sulfoxides imposes the approach of methyl lithioacetate, and therefore it enables the generation of optically active P-amino acids. ... 

Scheme 1.14 Allylation, benzylation, and alkenylation of N sulfinyl imines.

Kuninobu, Takai, and coworkers [90] demonstrated that aromatic imines undergo ortho alkenylation under Re catalysis (Scheme 18.88). This reaction was proposed to proceed via C-H bond activation at the ortho position of imines, alkyne insertion into not Re-H but Re-C bond, intramolecular nucleophihc attack of the formed Re-C(sp ) bond on an imino carbon, and final reductive eUmination. 

A unique rhodium-catalyzed oxidative alkenylation of diarylmethanols having a 2-(2-pyridyl) moiety with alkenes using silver carbonate as oxidant was reported (Scheme 4.99) [98]. The diarylmethanols also underwent a rhodium-catalyzed aldehyde-imine exchange reaction [99]. 

A simple and practical Cu(OTf)2-catalyzed synthesis of quinoline-2-carboxylates through tandem Grignard-type imine addition/Friedel-Crafts alkenylation of arenes with aryl or alkyl alkynes via activation of C-H bonds was reported in 2009 (Scheme 8.84). The quinoline-2-carboxylates products could be obtained in high yields from a number of readily available alkynes and imines at room temperature [154]. 

Furthermore, the asymmetric catalysis of 27 could accommodate vinylogous aza-enamines as a source of an alkenyl unit, and the use of 27d bearing the 2,6-dimethyl-4-(l-adamantyl)phenyl groups as catalyst led to the establishment of the general and highly enantioselective formal alkenylation of N-benzoyl imines [77]. Since the oxidative transformation of an aza-enamine moiety of the product into a nitrile functionality appeared feasible as described above, this method offered facile access to optically active y-amino a,P-unsaturated nitriles (Scheme 7.50). 

Lithium and zinc tert-butyl phenylmethyl sulfoxide (1) and A-phenyl imines 2, in which the substituent R is alkenyl or aryl, react at —78 °C over 2 hours with high anti diastereoselection (d.r. >98.5 1.5)6. Shorter reaction times result in poorer yields, due to incomplete reaction. In contrast, the reaction of the sulfoxide anion with benzaldehyde is complete after 5 seconds, but shows poor diastereoselection. When the substituent R1 or R2 of the imine 2 is aliphatic, the substrates exhibit poor chemical reactivity and diastereoselection. The high anti diastereoselection suggests that if a chelated cyclic transition state is involved (E configuration of the imine), then the boat transition state 4 is favored over its chair counterpart 5. 

Reduction of iV-(3-bromopropyl) imines gives a bromo-amine in situ, which cyclizes to the aziridine. Five-membered ring amines (pyrrolidines) can be prepared from alkenyl amines via treatment with N-chlorosuccinimide (NCS) and then BusSnH. " Internal addition of amine to allylic acetates, catalyzed by Pd(PPh3)4, leads to cyclic products via a Sn2 reaction. Acyclic amines can be prepared by a closely related reaction using palladium catalysts. Three-membered cyclic amines (aziridines)... 

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