A cationic oxazaborolidinium-catalyzed asymmetric Mukaiyama aldol reaction of (1-methoxy-2-methyl-propenyloxy)-trimethylsilane with various aldehydes including α,β-disubstituted acroleins has been developed in high yields and enantioselectivities. The synthetic utility of this methodology was demonstrated in the first short synthesis of naturally occurring inthomycin C in high enantiopurity.

A catalytic route toward chiral Morita-Baylis-Hillman esters by asymmetric coupling between alpha,beta-acetylenic esters, aldehydes, and trimethylsilyl iodide has been developed (see scheme). The reaction proceeds with high to excellent enantioselectivities, and the products can be transformed into beta-branched derivatives in a single step and with excellent retention of configuration. TMS = trimethylsilyl.

The anionic [4+2] cycloaddition of furoindolones with arynes and quinol ethers is introduced as an efficient strategy for the synthesis of indoloquinones. The utility of the strategy is exemplified by a very short synthesis of elipticine. Ellipticine (1), a representative member of pyrido [4,3-b]carbazole alkaloids, was isolated in 1959 from the stems of Ochrosia elliptica Labill. 1 In 1967, this alkaloid and its derivatives were reported to possess promising antitumour activities. 2 Since then, a large number of investigations of the structure-activity have been made concomitantly with the development of efficient synthetic routes to ellipticines and structurally allied derivatives. 3 Several ellipticine analogs are in phase II clinical trials, though the parent ellipticine is too toxic to be useful. However, elliptium, an ellipticine analog is used for treatment of thyroid, breast and kidney cancer. 4 Calothrixins (e.g., calothrixins A, 2), a newer class of alkaloids with an indolo[3,2-j]phenanthridine ring system were isolated from the cyanobacteria Calothrix in 1999. 5 They exhibit potent activity against both malaria parasites and human cancer cell lines at nanomolar scales. The striking structural resemblance between ellipticines and calothrixins provoked us to develop a common strategy for their synthesis. More interestingly, both calothrixin A (2) and ellipticine quinone (3, Figure 1) have very similar EC 50 values to HeLa cell lines. 6 Several indolonaphthoquinones also have shown promising antileukemic activity, but pharmacological studies are inhibited by the lack of easy accessibility. 7 Above all, simple indoloquinones are useful synthetic intermediates for the total synthesis of alkaloids. 8 Herein, we report our preliminary finding that the anionic [4+2] cycloaddition of furoindolones with arynes, quinol ethers and quinone monoketals provides a straightforward route for the preparation of indoloquinones. We also report that ellipticine (1) can be synthesized in only three steps from the known furoindolone 4, which, in turn, is obtainable in two steps from commercially available inexpensive starting materials.The established synthetic avenues to indoloquinones commonly entail Friedel-Crafts acylation or carbolithiation as one of the key steps. 9 Alternative methods rely upon use of 2-phenylamino-1,4-napthoquinones and formation of the heterocyclic ring as the last crucial step. 10 Our continued interest in the application of anionic [4+2] cycloaddition 11 of isobenzofuranones led us to undertake a study on anionic reactivity of furoindolones (e.g. 5). Moreover, anionic [4+2] cycloaddition has never been investigated in the context of heterocyclic quinone compounds. 12 Accordingly, we devised Scheme 1 for the direct entry to indoloquinones.Scheme 1 Proposed methodology for the synthesis of indoloquinones.