Imines with allenes

Other potential synthetic routes to these unsaturated aziridine derivatives which involve the addition of nitrenes to allenes <75JOC224), carbenes to imines with subsequent hydrolysis <67JA362), and of carbenoid species to ketenimines <76TL1317,79TL559) have been investigated but are collectively of little or no preparative value. 

Reversible pyridine dissociation yields the non-Lewis base stabilized imido complex [Cp(NHAr) Ti=NAr] (54). This coordinatively unsaturated species undergoes a [2 + 2] cycloaddition reaction with allene to give an azatitanocyclobutane (55), which is then protonated to the /mamido complex. Elimination of enamine occurs followed by isomerization to the energetically more favorable imine. 

A tertiary homopropargylic alcohol could also be prepared by treatment of ethyl acetate with two equivalents of B-allenyl-9-BBN. However, the reaction proceeded slowly and was not general for other esters, which proved to be unreactive, as were tertiary amides and alkyl halides. However, homopropargylic amines could be prepared in high yield and with minimal allenic byproduct through allenylboration of imines with B-allenyl-9-BBN (Eq. 9.24). 

Common reactions of the ylide include (i) [2,3]-sigmatropic rearrangement of allylic, propargylic, and allenic ylides (ii) [l,2]-shift (Stevens rearrangement) (iii) 1,3-dipolar cycloaddition of the ylide generated from carbonyl compounds or imines with dipolarophiles, usually G=G or C=C bonds and (iv) nucleophilic addition/elimination, leading to the formation of epoxides or cyclopropanes (Figure 2). 

The reaction of enamines and imines with acrylamide results in aza-annulation120,121. Other electrophilic alkenes which have been used to alkylate enamines and the products used in hetero- or carbocyclic synthesis include ethyl / -nitroacrylate122, where reaction occurs beta to the nitro not the ester group, 2-(phenylseleno)prop-2-enenitrile [CH2 = C(SePh)CN]123,124, phenyl a-phenylselenovinyl sulphone [CH2 = C(SePh)-S02Ph]124 and phenyl a-bromovinyl sulphone124. An electrophilic allene, phenylsulpho-nylpropadiene, has also been used to alkylate enamines125 (Scheme 44). 

The reaction between the imines and allenic titanium reagents give the anti adducts with high stereoselectivity (Scheme 36). The observed stereoselectivity can be explained by a cyclic transition state in which the metal coordinates to the lone pair of the nitrogen atoms. ... 

In 1963, Bestmann et al. disclosed that treatment of A-benzyhdeneaniline with semistabilized triphenylphosphonium ylides at 150-180 °C afforded alkenes, but with nonstabilized triphenylphosphonium ylides at 130-150 °C afforded allenes [219, 220]. For a long time this protocol had not been improved and developed into a useful stereoselective alkene synthesis, probably owing to the high reactiOTi temperature and inconvenient operation. Recently, Tian et al. have developed a highly trmable stereoselective olefination reaction of imines with triphenylphosphonium ylides at low temperature by employing sulfonyl groups to activate the imines [221-223]. 

In 2001, Gai et al. developed a palladium-catalyzed three-component cascade reaction for the synthesis of bis(2-arylallyl) tertiary amines from aryl iodides, allene, and primary amines [103] (Scheme 6.77). Aryl iodides react with allene to form a Jt-allylpalladium species 298 which is attacked by primary amines to obtain substituted allyl amines 299. The second nucleophilic attack of Jt-allylpalladium species 298 by amine 299 generates tertiary amines 297. Imines or other carbon nucleophiles can be introduced to this cascade reaction instead of primary amines, which is reported by the same group [104]. 

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

The reactive compound chlorosulfonyl isocyanate (ClSOaNCO, forms P-lactams even with unactivated alkenes, as well as with imines, allenes, conjugated dienes, and cyclopropenes. With microwave irradiation, alkyl isocyanates also... 

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