2-Amino-l ,3-butadiene

Barluenga et al. have described novel vinylcarbene complexes containing a cyclic BF2 chelated structure which temporarily fixes the s-cis conformation of the exocyclic C=C and Cr=C double bonds. These boroxycarbene complexes behave as dienophiles with 2-amino-l,3-butadienes in a remarkably regio- and exo-selective way. Moreover, high degrees of enantioselectivity are reached by the use of chiral 2-aminodienes derived from (S)-methoxymethylpyrrolidine [101] (Scheme 54). 

A combination of a Diels-Alder and a Fisher carbene-cyclopentannulation is described as the last example in this subgroup. Thus, Barluenga and coworkers used a [4+2] cycloaddition of 2-amino-l,3-butadienes 4-115 with a Fischer alkoxy-arylalky-nylcarbene complex 4-116 this is followed by a cyclopenta-annulation reaction with the aromatic ring in 4-116 to give 4-117 (Scheme 4.25) [36]. An extension of this domino process is the reaction of 4-118 with 2equiv. of the alkynyl carbene 4-119 containing an additional C-C-double bond (Table 4.2) [37]. The final product 4-120, which was obtained in high yield, is formed by a second [4+2] cycloaddition of the primarily obtained cyclopenta-annulated intermediate. 

Martin A, Garcia-Granda S, Martin E (1993) J Am Chem lective aza-Diels-Alder reactions of achiral 2-amino-1,3-znar F.Valdds C, Cabal M-P (1993) J Org Chem 58 3391 liral 2-amino-l,3-butadienes see Krohn K (1993) Angew a Int Ed Engl 32 1582 Enders D, Meyer 0 (1996) Liebigs... 

TABLE 6. 13C NMR chemical shifts [<5TMS (ppm)] for 2-amino-l,3-butadienes in CDC1,"... 

Enantiomerically pure 2-amino-l,3-butadiene 1 reacts with 2-aryl-l-nitroethenes 2 to yield adducts 3 with excellent enantioselectivities. Subsequent removal of the chiral auxiliary leads to nitrocyclohexanones 4 with good diastereoselectivity at the newly generated stereogenic center at C-2 and moderate yield23. 

Hetero-Diels-Alder reactions. The synthesis of 4-piperidones using Al-sily-laldimines as dienophiles is promoted by ZnCla- Excellent stereoinduction by a chiral moiety of 2-amino-l,3-butadienes is evident. ... 

Chiral 2-Amino-l,3-butadienes New Reagents for Asymmetric Cycloadditions... 

The synthesis of 2-aminobutadienes from ketones is somewhat limited due to difficult control of /Z-stereochemistry. [27] Therefore, the catalytic aminomercuration of3-alkenyl-l-ynes 4 was a significant improvement of the synthesis of 2-amino-l,3-butadienes 5 (yields 49-75 %). [28] The catalytic aminomercuration of 4-ethoxy-3-alkenyl-1-ynes even leads to electronrich and highly reactive 1,3-diamino-1,3-butadiens which undergo a great variety of cycloadditions. [29] Scheme 2 shows the reaction for a general example (for R = H two secondary amines can add to the enine 4 to yield 6). The method can easily be extended to the preparation of chiral 2-amino-1,3-butadienes by addition of chiral amines [e. g. (5)-2-methoxymethylpyr-rolidine (SMP) [27]]. 

Chiral 2-amino-l,3-butadienes derived from 2-(methoxymethyl)pyrrolidine and a-oxo enamines undergo cycloadditions with jV-silylimines in the presence of ZnCl2 to yield 4-piperidinones stereoselectively upon subsequent hydrolysis with aqueous NaHCOs. 

Amino-subsdnued dienes are also important dienophiles in Diels-Alder reactions Recently, chiral and achiral 2-amino-l,3-dienes have been prepared to snidy their reactivity Csee also asymmetric Diels-Alder reaction Section 8 1 2 The reaction of 2,3-diamino-l,3-butadienes v/ith nitrostyrene gives unusual [3t-2 carbocyclization products, 2-aminocyclopentanones, which are not formed by the direct cycloaddidon but derived from the Michael addidon products fsee secdon discussing the Michael addidon Secdon 4 1 3 "... 

Some 3-amino-1-butynes have been reported to rearrange in the vapor phase to the isomeric 2-amino-1,3-butadienes or when heated from 10° to 30°C above their boiling point [81] (Eq. 26). Similarly, l,4-bis(dialkylamino)-... 

An intramolecular aza Diels-Alder reaction of as well electronically neutral N-aryl imines useful for the synthesis of novel tetrahydropyridine derivatives has been introduced by our group [268]. The reactive intermediate 3-43 exhibiting the 2-aza-l,3-butadiene subunit was generated in situ from the aldehyde 3-41 and the amino isoxazole 3-42 and led directly to the diastereomerically pure cycloadduct 3-44 (Fig. 3-14). In contrast to the reactions studied by Barlu-enga, the 2-aza-1,3-butadiene acts as electron-deficient component in this case. 

Reaction of iV,A -unsubstituted selenoureas with a 1,2-diaza-l,3-butadiene affords 2-amino-4,5-dihydro-l,3-selenazol-4-ones 81 mainly in the hydrazono form. The reaction proceeds via nucleophilic addition of the selenium atom to the terminal carbon atom of the heterodiene. The subsequent intramolecular nucleophilic attack by the imidic NH at the carboxylate group with the loss of methanol leads to the selenazole ring closure (Scheme 14) <2002EJO2323, 2001SL144>. 

Interesting new 1,3-dienes for the Diels-Alder reaction include (Z)-l-phenylthio-2-methoxy-l, 3-butadiene, 3 2-methoxy-3-phenylthio-l, 3-butadine, 11 and N-acyl-l-amino-1,3-butadiene 115... 

The Diels-Alder chemistry of chiral amino-l,3-butadienes has recently been reviewed and has been the subject of sevaal studies since. For instance, Enders and Klatt studied the reactions between chiral diene 305 carrying (5)-2-methoxymethylpyrrolidine as... 

The synthesis of Ilia starts from the unknown 4-nitrocyclohexanone, which was achieved by a Diels-Alder reaction between nitroethylene and 2-(trimethylsilyloxy)-l,3-butadiene, and following the sequence depicted in Scheme 34, vinyl bromide 112a was obtained. This amino-tethered ketone vinyl halide was treated with 0.2 equiv of Pd(PPh3)4 and 1.5 equiv of KOt-Bu at reflux temperature (THF) for 30 min to give the azatricyclic compound 111a in 54% yield. 

The anion (2) also reacts with ketones to give, after hydrolysis, alkylideneamino alcohols (5). On treatment with acid 5 is converted into -amino alcohols (6) on dehydration 2-aza-l, 3-butadienes (7) are formed. 

Acetaldehyde, acrolein, 2-aminobutane, 2-amino-2-methylpropane, 2-bromo-2-chloro-l,l,l-tri luoroethane, bromomethane, 1,3-butadiene, l-chloro-l,l-difluoro-ethane, chlorofluoromethane, 2-chloro-l,3-butadiene, chloroform, 3-chloro-l-pro-... 

Reactions of 2-aza-l,3-butadienes with electron-donating substituents and chiral nitroso compounds take place selectively in the absence of Lewis acids at low temperature. The cycloadducts are useful precursors of a-amino acids. 

Aznar, et al. reported a proline-catalyzed imino-Diels-Alder reactions of acyclic a,p-unsaturated ketones 96 with imines 92 for the synthesis of mc50-2,5-diaryl-4-piperidones 98, Scheme 3.35 [50], The 2-amino-1,3-butadiene was generated in situ by the reaction of a,p-unsaturated ketones 96 with L-proline, followed by Diels-Alder cycloaddition with imine 92 to provide tetrahydropyridine adduct which was then hydrolyzed to the 4-piperidone 98. 

DAB 155a-c and 2,3-DAN 235 on the terminal carbon of the heterodiene system of 1,2-diaza-l,3-butadienes 246 with the formation of the hydrazone 1,4-adduct (Michael type) 250. The subsequent nucleophilic attack of the second amino group at the hydrazone carbon with the loss of a hydrazine carboxylate residue results in 2-phosphorylated quinoxalines 251a-i. This strategy affords a very efficient entry to quinoxaline phosphine oxides 251a, c, e-h and phosphonates 251b,... 

Marko, l.E. and Chesney, A. (1992) Towards the total synthesis of manzamines preparation and reactions of 2-methoxycarbonyl-l,3-butadienes and P-amino aldehydes, Synlett, 275-278. 

The enantioselective intramolecular formal 2+4-cycloaddition of acrylates and a, -unsaturated imines (99) catalysed by chiral phosphines (100), derived from amino acids, produced A-heterocycles (101) (Scheme 31). Chiral dirhodium(II) carboxamidates (102) catalysed the hetero-Diels-Alder reactions between 2-aza-3-silyloxy-l,3-butadienes and aldehydes to yield all cw-substituted l,3-oxazinan-4-ones in high yields and high enantioselectivity (98% ee)P The nickel-catalysed 4 + 2-cycloaddition of a, -unsaturated oximes with alkynes yielded 2,3,4,6-tetrasubstituted pyridine derivatives. The reaction of isoquinoline, an activated alkyne, and 4-oxo-4//-l-benzopyran-3-carboxaldehyde (103), in ionic solvents, produced 9a//,15//-benzo[a][l]benzopyrano[2,3-/t]quinolizine derivatives (105) via the zwitterion (104) selectively and in good yields (Scheme 32).The Diels-Alder cycloaddition of ethyl 3-(tetrazol-5-yl)-l,2-diaza-l,3-butadiene-l-carboxylates with -rich heterocycles, nucleophilic olefins, and cumulenes formed 3-tetrazolyl-l,4,5,6-tetrahydropyridazines regioselectively. The silver-catalysed formal inverse-electron-demand Diels-Alder... 

The domino process probably involves the chiral enamine intermediate 2-817 formed by reaction of ketone 2-813 with 2-815. With regard to the subsequent cy-doaddition step of 2-817 with the Knoevenagel condensation product 2-816, it is interesting to note that only a normal Diels-Alder process operates with the 1,3-bu-tadiene moiety in 2-817 and not a hetero-Diels-Alder reaction with the 1-oxa-l,3-butadiene moiety in 2-816. The formed spirocydic ketones 2-818/2-819 can be used in natural products synthesis and in medidnal chemistry [410]. They have also been used in the preparation of exotic amino adds these were used to modify the physical properties and biological activities of peptides, peptidomimetics, and proteins... 

Honciuc A, Jaiswal A, Gong A, Ashworth K, Spangler CW, Peterson IR, Dalton LR, Metzger RM (2005) Current rectification in a Langmuir-Schaefer monolayer of fullerene-bis-[4-diphenylamino-4 -(N-ethyl-N-2 -ethyl)amino-l,4-diphenyl-l,3-butadiene] malonate between Au electrodes. J Phys Chem B109 857-871... 

Sudo and Saigo153 reported the application of ds-2-amino-3,3-dimethyl-l-indanol derived l,3-oxazolidin-2-one 231 as a chiral auxiliary in asymmetric Diels-Alder reactions. The TV-crotonyl and TV-acryloyl derivatives were reacted with cyclopentadiene, 1,3-cyclohexadiene, isoprene and 2,3-dimethyl-l,3-butadiene, using diethylaluminum chloride as the Lewis acid catalyst. The reactions afforded the expected cycloadducts in moderate to high yields (33-97%) with high endo selectivities and high de values (92% to >98%). 

Diazadienes 314 (R2 = Ph) afforded, in the same way, good yields of bis-trifluoromethyl dihydroquinazolines 335, as reported by Burger and Penninger (Scheme 74). However, N-unsubstituted heterodienes 314 (R2 = H) yielded upon heating with aromatic nitriles symmetrical triazine derivatives 336 through a [4 + 2] cycloaddition (78S524). Muchowski and co-workers have employed the related 2-trichloromethyl-4-dimethyl-amino-1,3-diaza-l, 3-butadienes 337 for synthesizing 2-trichloromethylpyr-imidines 338 in 38-98% yield by cyclization with electron-deficient acetylenes moreover, triazine 339 was obtained in 80% yield in the reaction of... 

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