The chemical transliteration of Plato's universe-the dodecahedrane-has been synthesized in 23 steps. The key stages of the sequence starting from dichloro diester 2 involve the following: (a) reduction-monoakylation of 2 using chloromethyl phenyl ether to give 7; (b) photocyclization of aldehyde 12 without interference from the geminal side chain; (c) retro-aldol cleavage of keto aldehyde 15; and (d) catalytic dehydrogenation of 19. The single-peak nature of the 'H and 13C NMR spectra of 1 conforms to its ultrahigh (I,,) symmetry. The spherical hydrocarbon exhibits three infrared-active and eight Raman-active bands. The unique physical behavior of 1 upon heating to temperatures above 400 OC is detailed.For centuries, the dodecahedron has been esteemed as the most complex and aesthetically pleasing of the perfect solids of antiquity. In more recent times, scientists have come to regard its molecular transliteration, dodecahedrane (C2,,HH,, 1), as the "Mount Everest u

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Treatment of suitable alpha‐hydroxy aldehydes and ketones with a base, a Bronsted or Lewis acid, or simply with heat has long been know to induce the 1,2‐shift of an alkyl or aryl substituent to form an isomeric product. The synthetic utility of the process was considerably expanded when applied to steroidal D‐ring homoannulations, and has more recently encompassed novel ring expansion to numerous complex target ring systems. The classical alpha‐ketol rearrangement shares, in common with other base‐promoted ketogenic isomerizations, the property of advancing from an alkoxide to a carbonyl group as the migrating center relocates its bonding electrons to the adjacent trigonal center. A distinctive feature of the title reaction, however, is its reversibility, such that the more stable alpha‐hydroxy carbonyl isomer is favored. The process has sometimes been termed the acyloin rearrangement. This chapter focuses on the isomerization of alpha‐hydroxy ketones, aldehydes, and imines under various reaction conditions exclusive of photochemical activation. The literature coverage extends to 2000. Since many of the steroidal transformations were carried out in early days when products were not always adequately characterized; errors in structural assignment were occasionally made. Experimental detail was sometimes lacking. To alleviate this problem, we have included only experiments that lead to reasonably pure products of established structure.

An enantioselective synthetic route to the thermodynamically most stable diastereomer of the structure assigned to sclerophytin A (5) has been realized. The required tricyclic ketone 33 was prepared by sequential Tebbe-Claisen rearrangement of lactones 29 and 30, which originated from the Diels-Alder cycloaddition of Danishefsky's diene to (5S)-5-(d-menthyloxy)-2(5H)-furanone (14). An allyl and a cyano group were introduced into the resulting adduct by means of stereocontrolled allylindation under aqueous Barbier-like conditions and by way of cyanotrimethylsilane, respectively. Following stereocontrolled nucleophilic addition of a methyl group to 33, ring A was elaborated by formation of the silyl enol ether, ytterbium triflate-catalyzed condensation with formaldehyde, O-silylation, and Cu(I)-promoted 1,4-addition of isopropylmagnesium chloride. The superfluous ketone carbonyl was subsequently removed and the second ether bridge introduced by means of oxymercuration chemistry. Only then was the exocyclic methylene group unmasked via elimination. An alternative approach to the alpha-carbinol diastereomer proceeds by initial alpha-oxygenation of 37 and ensuing 1,2-carbonyl transposition. Neither this series of steps nor the Wittig olefination to follow induced epimerization at C10. Through deployment of oxymercuration chemistry, it was again possible to elaborate the dual oxygen-bridge network of the target ring system. Oxidation of the organomercurial products with O(2) in the presence of sodium borohydride furnished 72, which was readily separated from its isomer 73 after oxidation to 61. Hydride attack on this ketone proceeded with high selectivity from the beta-direction to deliver (-)-60. Comparison of the high-field (1)H and (13)C NMR properties and polarity of synthetic 5 with natural material required that structural revision be made. Following a complete spectral reassessment of the structural assignments to many sclerophytin diterpenes, a general approach to sclerophytin A, three diastereomers thereof, and of sclerophytin B was devised. The presence of two oxygen bridges as originally formulated was thereby ruled out, and absolute configurations were properly determined. Key elements of the strategy include dihydroxylation of a medium-ring double bond, oxidation of the secondary hydroxyl in the two resulting diols, unmasking of an exocyclic methylene group at C-11, and stereocontrolled 1,2-reduction of the alpha-hydroxy ketone functionality made available earlier.