Stereoselective synthesis and relative configuration assignment of gabosine J

Concise Synthesis of (1R,2S,3R,6R)-6-Ethoxy-4-(hydroxymethyl)cyclohex-4-ene-1,2,3-triol, a Key Intermediate for the Synthesis of Uvacalols I and J

Uvacalols are novel carbasugars isolated from the genera Uvaria. In this study, we report concise syntheses of (1R,2S,3R,6R)-6-ethoxy-4-(hydroxymethyl)cyclohex-4-ene-1,2,3-triol, a key intermediate for the synthesis of uvacalols I and J, and of its epimer (1R,2S,3S,6R)-6-ethoxy-4-(hydroxymethyl)cyclohex-4-ene-1,2,3-triol, starting from cheap and readily available methyl d-glucopyranoside.

Enantioselective Synthesis of a New Non-Natural Gabosine

The preparation of a new non-natural gabosine is reported, in which the chirality is transferred from the toluene’s biotransformed metabolite (1R,2S)-3-methylcyclohexa-3.5-diene-1,2-diol. Further chemical transformations to introduce additional functionality and chirality to the molecule were also accomplished.

A divergent strategy to synthesize gabosines featuring a switchable two-way aldol cyclization

Gabosines and their natural analogues, belonging to C7 carbasugars, have attracted great attention in synthesis due to their rich structural variety and promising biological activities. A new diversity-oriented approach for the gabosine-type carbasugars based on a tunable regioselective aldol cyclization of flexible precursor 2 is explored. Two cyclization modes (A and B) of the precursor can be well controlled by switching promoters to selectively produce two resulting cyclohexa(e)nones 3 and 10, both of which are versatile intermediates for various C7 carbasugars. After the conversion of 3 to eight natural carbasugars, the utility of intermediate 10 is illustrated by the first synthesis of (-)-gabosine L, as well as the new synthesis of (-)-gabosine A, (-)-gabosine B, (-)-gabosine N and (-)-gabosine O. The chemical structure and the absolute configuration of (-)-gabosine L are confirmed by its total synthesis.

Stereodivergent and enantioselective total syntheses of isochaetominines A–C and four pairs of isochaetominine C enantiomers: a six-step approach

We report the first total syntheses of (−)-isochaetominines A–C and eight 2,3-cis-stereoisomers of isochaetominine C, and structural revisions of (−)-pseudofischerine and (−)-aniquinazoline D.

Total syntheses of five uvacalols: structural validation of uvacalol A, uvacalol B and uvacalol C and disproval of the structures of uvacalol E and uvacalol G

Uvacalols are novel carbasugars belonging to the family of C7-cyclitols, and are isolated from the roots of the medicinal plant, Uvaria calamistrata. In this study, we report the first syntheses of five uvacalols starting from a cheap and easily available chiral pool starting material, D-mannitol, in their optically pure form. D-Mannitol was converted to the alkene 2 through a series of regioselective and chemoselective transformations by following our previously reported strategies. Alkene 2 was converted to the enal 5 through a series of protective group manipulations. Enal 5 was converted to the diene 6 by the addition of vinyl magnesium bromide. Ring closing metathesis of the diene 6 using Grubbs’ second generation catalyst installed the core cyclohexenyl unit. Through several iterative and selective manipulations of various hydroxyl groups, uvacalol A, uvacalol B, uvacalol C, uvacalol E and uvacalol G were synthesized. A comparison of the (1)H NMR and (13)C NMR data of these synthesized molecules with the reported data, revealed that the reported structures of uvacalols A–C are correct and those of uvacalols E and G are wrong.

Total syntheses and structural validation of lincitol A, lincitol B, uvacalol I, uvacalol J, and uvacalol K

First total syntheses of lincitol A, lincitol B, uvacalol I, uvacalol J and uvacalol K were achieved in racemic form, validating their structure from a common intermediate, which was synthesized in six steps from low-cost and extensively available myo-inositol.

How a diversity-oriented approach has inspired a new hypothesis for the gabosine biosynthetic pathway. A new synthesis of (+)-gabosine C

A new synthesis of (+)-gabosine C has been accomplished as part of a general diversity-oriented approach that also delivered the previously unknown (-)-4-epi-gabosine C. The identification of the unexpected intermediate (+)-8, together with the isolation of ketones 9 and 10 in previous investigations, prompted us to formulate a new hypothesis for the biosynthesis of gabosines, based on a keto-enol equilibrium cascade pathway starting from 2-epi-5-epi-valiolone, along which the necessary precursors for all the different types of gabosines are generated.

New Ag(I)-iminophosphorane coordination polymers as efficient catalysts precursors for the MW-assisted Meyer-Schuster rearrangement of propargylic alcohols in water

Treatment of the N-thiophosphorylated iminophosphorane ligands (PTA)═NP(═S)(OR)2 [PTA = 1,3,5-triaza-7-phosphaadamantane, 3a and 3b] and (DAPTA)═NP(═S)(OR)2 [DAPTA = 3,7-diacetyl-1,3,7-triaza-5-bicyclo[3.3.1]nonane, 4a and 4b] with an equimolecular amount of AgSbF6 leads to high-yield formation of the new one-dimensional coordination polymers [Ag{μ(2)-N,S-(PTA)═NP(═S)(OR)2}]x[SbF6]x (5a and 5b) and [Ag{μ(2)-O,S-(DAPTA)═NP(═S)(OR)2}]x[SbF6]x (6a and 6b), respectively. These new (iminophosphorane)silver(I) coordination polymers are efficient catalyst precursors for the Meyer-Schuster isomerization of both terminal and internal alkynols. Reactions proceeded in water, under aerobic conditions and using microwave irradiation as heating source, to afford the corresponding α,β-unsaturated carbonyl compounds in excellent yields, without the addition of any cocatalyst. Remarkably, it should be noted that this catalytic system can be recycled up to 10 consecutive runs (1st cycle 45 min, 99%; 10th cycle 6 h, 97%). ESI-MS analysis of 5a in water has been carried out providing valuable insight into the monomeric active species responsible for catalytic activity in water.