An asymmetric, organocatalytic, one-pot Mannich cyclization between a hydroxylactam and acetal is described to provide fused, bicyclic alkaloids bearing a bridgehead N atom. Both aliphatic and aromatic substrates were used in this transformation to furnish chiral pyrrolizidinone, indolizidinone, and quinolizidinone derivatives in up to 89% yield and 97% ee. The total syntheses of (-)-epilupinine, (-)-tashiromine, and (-)-trachelanthamidine also achieved to demonstrate the generality of the process.

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We report a highly efficient, enantioselective, organocatalytic method for the synthesis of izidinone alkaloids containing a bridgehead aza-quaternary center using ketone-derived N,O-hemiaminal with a tethered acetal. Alkyl-, aryl-, and alkenyl-substituted substrates cyclize to the respective products with excellent enantioselectivities. Five- and seven-membered ring formation has also been established. Furthermore, synthesis of the tricyclic skeleton of cylindricine alkaloids has been achieved in high yield.

An asymmetric, organocatalytic, one-pot Mannich cyclization between a hydroxylactam and acetal is described to provide fused, bicyclic alkaloids bearing a bridgehead N atom. Both aliphatic and aromatic substrates were used in this transformation to furnish chiral pyrrolizidinone, indolizidinone, and quinolizidinone derivatives in up to 89 % yield and 97 % ee. The total syntheses of (À)-epilupinine, (À)-tashiromine, and (À)-trachelanthamidine also achieved to demonstrate the generality of the process.Naturally occurring izidine alkaloids (pyrrolizidine, indolizidine, and quinolizidine; Figure 1 A) and their synthetic variants are of considerable importance because of their diverse biological activities.[1] While the polyhydroxylated izidines inhibit glycosidase and glycosyl-transfer enzymes, and show anti-HIV, anti-dengue virus, anticancer, antiinflammatory, and antidiabetic activities, [2] the alkylated izidines are noncompetitive blockers of nicotinic acetylcholine receptors and are known as defense chemicals used by hosts against predators. [3] Although chiral-pool [4,5] and chiral-auxiliary-mediated [4,6] approaches have been described for the asymmetric synthesis of various izidine derivatives, they are often target directed. In contrast, approaches for the catalytic asymmetric synthesis of these skeletons are limited and izidine specific. These include chiral-rhodium-catalyzed [7] [2+2+2], [3+3], and 1,3-dipolar cycloadditions for indolizidine and quinolizidine derivatives, asymmetric hydrogenation of dihydro-b-carbolines, [8] organocatalytic cascade cyclizations, [9] formal azahetero-Diels-Alder reactions, [10] intramolecular annulation of oxo-isoquinolinium [11] for quinolizidine derivatives, chiralsilver-catalyzed one-pot double 1,3-dipolar cycloaddition for pyrrolizidines, [12] and asymmetric hydrogenation of indolizine by a chiral-ruthenium-catalyst [13] for indolizidine derivatives. A few other examples of enantioselective organocatalytic reactions are also known for the synthesis of indolizidinebased alkaloids.[14] However, a general method for the catalytic asymmetric synthesis of all the izidine skeletons is rare. Herein, we report the development of an asymmetric organocatalytic Mannich cyclization for the synthesis of the bicyclic skeleton of izidine alkaloids and its application to the total syntheses of (À)-epilupinine, [15] (À)-tashiromine, [16] and (À)-trachelanthamidine. [17] Inspired by the biosynthetic pathway of pyrrolizidine alkaloids (1 a!1 b; Figure 1 B), [18] we recently reported the Brønsted acid catalyzed Mannich cyclization between a hydroxylactam and acetal (2 a!(rac)-2 b; Figure 1 B). [19] This reaction led us to realize that an asymmetric version of such a cyclization might be possible by using a suitable chiral catalyst. Although various chiral Brønsted acid [20] catalyzed enantioselective reactions of N-acyliminium [20,21] ions with various aromatic and heteroaromatic C nucleophiles [20,22] have been reported, these processes are unable to introduce chirality at...

In this paper mainly we have obtained equivalent conditions on skew semi rings, regular semi near rings and Idempotent semi near rings. Key words:skew semi rings, regular semi near rings and Idempotent semi near rings. introduction:-In this paper we obtained certain Identities on regular semi near rings and also we have obtained certain equivalences on semi near rings,regular semi near ring, and Idempotent semi near rings. We also obtained results such as x +x ≈ x, xy + yx + xy ≈ xy , y +yx + y ≈ y, xyx + xy + xyx ≈ xyx, yxy + xyx + yxy ≈ yxy, x + xyx + x ≈ x using the identities xx ≈ x, x + xy + x ≈ x, x + yx + x ≈ x. Also by using Greens is relation (i.