Novel rearrangements of 4-silyl-3-buten-2-ones

Propargylation of CoQ0 through the Redox Chain Reaction

An efficient catalytic propargylation of CoQ0 is described by employing the cooperative effect of Sc(OTf)₃ and Hantzsch ester. It is suggested to work through the redox chain reaction, which involves hydroquinone and dimeric propargylic moiety intermediates. A broad range of propargylic alcohols can be converted into the appropriate derivatives of CoQ0 containing triple bonds in good to excellent yields. The mechanism of the given transformation is also discussed.

DMSO/SOCl2-mediated C(sp2)-H amination: switchable synthesis of 3-unsubstituted indole and 3-methylthioindole derivatives

The reaction of 2-alkenylanilines with SOCl2 in DMSO was found to selectively afford 3-unsubstituted indoles and 3-methylthioindoles. This switchable approach was found to be temperature-dependent: at room temperature, the reaction afforded 3-unsubstituted indoles through intramolecular cyclization and elimination; while at higher temperature, the reaction gave 3-methylthioindoles via further electrophilic methylthiolation.

Divergent Synthesis of Vinyl-, Benzyl-, and Borylsilanes: Aryl to Alkyl 1,5-Palladium Migration/Coupling Sequences

Organosilicon compounds have been extensively utilized both in industry and academia. Studies on the syntheses of diverse organosilanes is highly appealing. Through-space metal/hydrogen shifts allow functionalization of C-H bonds at a remote site, which are otherwise difficult to achieve. However, until now, an aryl to alkyl 1,5-palladium migration process seems to have not been presented. Reported herein is the remote olefination, arylation, and borylation of a methyl group on silicon to access diverse vinyl-, benzyl-, and borylsilanes, constituting a unique C(sp³ )-H transformation based on a 1,5-palladium migration process.

Recent advances in transition metal-free catalytic hydroelementation (E = B, Si, Ge, and Sn) of alkynes

This review describes the recent advances in the transition metal-free hydroelementation of alkynes with various metalloid hydrides.

Palladium-Catalyzed Desulfitative Oxidative Coupling between Arenesulfinic Acid Salts and Allylic Alcohols: A Strategy for the Selective Construction of β-Aryl Ketones and Aldehydes

An efficient palladium-catalyzed desulfitative oxidative coupling of sodium arylsulfinites for highly region-selective Heck-type reaction of allylic alcohols has been developed. The compatibility of the functionalities of -I, -Br, and -F would explore further postfunctionalization of the C-X bonds. This method provides a new and straightforward protocol for the synthesis of β-aryl ketones and aldehydes. The deuterium labeling experiments indicated that this transformation may proceed via a [1, 2-H] shift process.

Structure determination of bisacetylenic oxylipins in carrots (Daucus carota L.) and enantioselective synthesis of falcarindiol

Although bisacetylenic oxylipins have been demonstrated to exhibit diverse biological activities, the chemical structures of many representatives of this class of phytochemicals still remain elusive. As carrots play an important role in our daily diet and are known as a source of bisacetylenes, an extract made from Daucus carota L. was screened for bisacetylenic oxylipins, and, after isolation, their structures were determined by means of LC-MS and 1D/2D NMR spectroscopy. Besides the previously reported falcarinol, falcarindiol, and falcarindiol 3-acetate, nine additional bisacetylenes were identified, among which six derivatives are reported for the first time in literature and three compounds were previously not identified in carrots. To determine the absolute stereochemistry of falcarindiol in carrots, the (3R,8R)-, (3R,8S)-, (3S,8R)-, and (3S,8S)-stereoisomers of falcarindiol were synthesized according to a novel 10-step total synthesis involving a Cadiot-Chodkiewicz cross-coupling reaction of (S)- and (R)-trimethylsilanyl-4-dodecen-1-yn-3-ol and (R)- and (S)-5-bromo-1-penten-4-yn-3-ol, respectively. Comparative chiral HPLC analysis of the synthetic stereoisomers with the isolated phytochemical led to the unequivocal assignment of the (Z)-(3R,8S)-configuration for falcarindiol in carrot extracts from Daucus carota L.

Selective oxidation of zirconocyclopentenes via organoboranes

[reaction: see text] A new, convenient, one-pot protocol is described for oxidation of zirconocyclopent-2-enes selectively at the sp(3) carbon by efficient transfer to electrophilic ((c)Hex)(2)BCl followed by oxidation with H(2)O(2)/NaOH to afford 1-alkylidene-2-hydroxymethylcyclopentanes. Results with several substrates show that overall reaction efficiencies for the zirconocene-mediated enyne cyclization, boron transmetalation, and oxidation sequence are generally comparable to yields obtained from protonation of intermediate zirconocycles. The formation of E/Z olefin isomers from the cyclization-oxidation sequence and an acid-catalyzed pinacol-type rearrangement of a vinylsilane are described.

Synthetic approach to the AB ring system of ouabain

Several novel hydroxylated cis-decalin derivatives, potential intermediates for the synthesis of the AB ring system of the important cardiotonic steroid ouabain, have been synthesized from commercially available starting materials. The first step in the preparation of these highly functionalized intermediates is a Robinson annulation of the beta-keto ester 6 and the 4-silyl-3-buten-2-one 5 to furnish the octalone 4 with good diastereoselectivity in fair yield (due to competition with a novel silicon-to-carbon phenyl migration). Reduction of the epoxy alcohol 3 (derived from 4 in two high-yielding steps) with LiAlH(4) gave a mixture of the desired triol 11 along with the product of an unusual reductive opening at the tertiary carbon, namely the triol 12. A plausible mechanism for this unusual reduction is presented as are possible methods for avoiding it. In particular, reduction of the corrresponding epoxy ketone 15 with aluminum amalgam proceeded in good yield to give the hydroxy ketone 16. Also reduction of the epoxide ester having the inverted stereochemistry at C3 afforded the desired tertiary alcohol 33 in good yield. Another approach using the beta,gamma-unsaturated ketal 38 permitted the formation of the tertiary alcohol 40. Fleming oxidation of the related, very functionalized silane 39 afforded the desired 1beta-alcohol 41 in fair yield. Finally a novel rearrangement was observed when the epoxy alcohol 24 was treated with DIBAL to effect loss of the angular hydroxymethyl group to produce the tetrasubstitued alkene 29 in high yield.