1.3- Dienamines, cyclic

The dienamine (148) can react in two ways with methane sulfonyl chloride. In one a 1,4 Diels-Alder-type addition gives 149 in the other way the initially formed product reacts further to give the bis-cyclic sulfone (150) (102,103). 

While the usual eonsequence of hydration of enamines is eleavage to a secondary amine and an aldehyde or ketone, numerous cases of stable carbinolamines are known (102), particularly in examples derived from cyclic enamines. The selective terminal hydration (505) of a cross-conjugated dienamine-vinylogous amide is an interesting example which gives an indication of the increased stabilization of the vinylogous amide as compared to simple enamines, which is also seen in the decreased nucleophilicity of the conjugated amino olefin-carbonyl system. 

Olefins are also the products of hydroboratlon of enamines, followed by treatment of the organoborane products with hot acid (543,544). The reduction of enamines with sodium borohydride and acetic acid (545) and the selective reduction of dienamines with sodium borohydride to give homo-allylic tertiary amines (138-140,225,546,547), has been applied to the synthesis of conessine (548) and other aminosteroid analogs (545,549-552). Further examples of the reduction of imonium salts by sodium borohydride can be found in the reduction of Bischler-Napieralski products, and other cyclic imonium salts (102). 

Enaminone 128 (Scheme 33) is obtained, together with an isomeric indo-lizine derivative, by flash vacuum thermolysis of aminomethylene Meldrum s acid derivative through intermediate ketene and delocalized azomethine ylide (85TL833). The thermally induced cyclization of semi-cyclic dienamines to afford, for instance, tricyclic 129 is also believed to start with an azomethine ylide (97JOC7744) the p-chlorophenyl substituent is essential for the reaction. Unstabilized ylide 130, on the other hand, is generated from pipecolinic acid and /1-phenylcinnamaldehyde by the decarboxylation method target base 131 is formed by 1,7-electrocycliza-tion and [l,5]-hydrogen shift (99J(P1)2605). 

Thiete sulfones show an irregular behavior pattern when involved in cycloaddition reactions. With 1,3-dienes, dienamines, enamines, ynamines, diazoalkenes, cyclopropadiene, and its substitution products, furan, and anthracene, the addition proceeds in the normal fashion. With certain Diels-Alder reagents such as tetraphenylcyclopentadienone (tetracycloneX however, the cyclic sulfones react anomalously. The Diels-Alder adducts undergo decomposition with SO 2 and CO extrusion to a seven-membered ring, the tetraphenylcycloheptatriene 223. Bicyclic octadienone is produced as well (Eq. 62). The mechanism of this unusual reaction is proposed by... 

The first isolation of a 5-amino-l-tosyltriazoline from the action of tosyl azide on a cyclic dienamine at low temperature has been reported recently (Scheme 59).240... 

TABLE 15. H-NMR chemical shifts [<5TMS (ppm)] for simple cyclic dienamines in CDC13... 

Cyclic non-conjugated (139 and 140) or conjugated (141 and 142) dienamines may be obtained by Birch reduction of the corresponding aromatic amine552,553. The preferred conditions involve the use of lithium and t-pentyl alcohol rather than ethanol, since the latter tends to give a considerably higher proportion of the further reduced tetrahydro derivative554. 

With dienamines, [4+2] cycloaddition may compete with the generally favoured [2+2] cycloaddition, as occurs with the acyclic dienamine (103), which yields a mixture of the [4+2] adduct (104) and the [2+2] adduct (105) (Scheme 69). On the other hand, when the cyclic cisoid dienamine (106) is used, the [4+2] cycloadduct (107) is the sole product (Scheme 70). 

The proton chemical shifts of representative acyclic and cyclic dienamines are collected in Tables 14-16. Examination of the Tables show that alkenyl substitution at C(l) or C(2) of an enamine produces also deshielding of the olefinic protons, as seen by comparing the <5H(2) values of compound 149 (3 3.75, 3.85 ppm Table 11) with those of the analogous cross-conjugated dienamine 105 ( 3.85, 4.05 ppm Table 14). The chemical shift of the vinylic protons of dienamines correlate only partially with the charge calculated for the corresponding olefinic carbons . In the linear conjugated... 

Mixtures of linear (130a and I30b) and cross-conjugated (131a and 131b) dienamines have also been obtained from cyclic , -unsaturated ketones (equation 35). A similar mixture is formed by dimerisation of enamines derived from methyl alkyl ketones and ketals (equation 36). 

Oxidation. P-Enamino carboxamides derived from cyclic p-keto amides are oxidized by Mn(OAc)j-Cu(OAc)2 to give enones, dienamines, or aniline derivatives, depending on the ring size. 

Dienamines show interesting behavior towards sulfene. With the acyclic dienamine 105, [4 + 2] cycloaddition was found to compete with the usual [2 + 2] cycloaddition (equation 79)194 195 whereas the cyclic dienamine 106, in which the cisoid structure is fixed, gave only the [4 + 2] cycloadduct (equation 80)196. Addition of sulfene to 1-dimethylamino-l,3-cyclooctadiene (107) has been shown to give a mixture of products (108,109,110 and products derived from further reaction of 110), depending upon reaction conditions (equation 81)197. 

Aleman, Fraile and coworkers described 1,3-dipolar cycloadditions of unsaturated aldehydes and cyclic azomethine imines (Scheme 8.36). The reaction proceeds either via iminium or dienamine activation of the corresponding aldehyde, giving chiral tetrahydroisoquinoline derivatives. Interestingly, it can be controlled either by the structure of the dipole or by additives such as tetrabutylammonium bromide. This transformation was investigated also by Du, Wang and coworkers. ... 

Azeotropic water entrainment s. 18, 454 cyclic 1,3-dienamines s. I. Seki, Chem. Pharm. Bull. 18, 671 (1970)... 

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