Synthesis of a Small Repertoire of Non-Racemic 5a-Carbahexopyranoses and 1-Thio-5a-carbahexopyranoses

Abstract

A short and practical entry to optically pure 5a-carbahexopyranose and 1-thio-5a-carbahexopyranose representatives is described. Besides a few functional group and protecting group manipulations, the synthetic scheme counts on two fundamental carbon−carbon bond-forming reactions, namely (i) a regio-and stereoselective aldol addition between heterocyclic (silyloxy)diene donors (6 or 13) and D-glyceral-

The Vinylogous Aldol and Related Addition Reactions: Ten Years of Progress

“…Following a preparative work aimed at optimizing the crucial intermolecular vinylogous aldolization and the intramolecular ring-forming aldolization, 83 total syntheses of 5a-carbapyranose, 4a-carbafuranose, 1-sulfanyl-5a-carbapyranose, and 1-sulfanyl-4a-carbafuranose compounds 165-168 were realized by using 2,3-O-isopropylidene-D-glyceraldehyde (169) as the common three-carbon synthon (Schemes 29 and 30). 84, 85 For β-D-gulo-carbapyranose 165 (Scheme 29, eq 1), the opening ploy was a highly diastereoselective BF 3 169, producing butenolide adduct 170 in 75% isolated yield and 85:15 diastereoselectivity in favor of the 5,1 0 -syn-1 0 ,2 0 -anti-configured isomer (5R,1 0 S,2 0 R). Conventional chemistry transformed 170 to aldehyde 171 that was advanced to bicyclic compound 172 by using a direct, highly productive, and silylative cycloaldolization maneuver assisted by the TBSOTf/DIPEA Lewis acid/Lewis base mixture.…”

Advances in Exploring Heterocyclic Dienoxysilane Nucleophiles in Asymmetric Synthesis

“…Schemes 4 and 5 briefly highlight the synthesis of the products in this venture. 15,16 Since the essential chemistry was similar, only a slight variation of the protocol was required, with marginal adaptation to the targets. Thus, b-Dgulocarbapyranose 16, b-D-xylocarbafuranose 19 (Scheme 4), as well as the sulfur-containing congeners 24 and 27 (Scheme 5) were targeted, exploiting siloxyfuran 12 and siloxythiophene 20 as the initial building blocks.…”

“…As shown in Scheme 8, a generic cycloheptane amino acid is disconnected along three bonds, C5-C6, C3-C9, Scheme 5 Total synthesis of 1-sulfanyl-5a-carbapyranose 24 15 and 1-sulfanyl-4a-carbafuranose 27 16…”

Asymmetric syntheses of (−)-methyl shikimate and (−)-5a-carba-β-d-gulopyranose from d-arabinose via Mukaiyama-type intramolecular aldolization

“…The mixture was stirred at room temperature for 12 h, and then was heated at reflux. After stirring was continued at reflux for 16 h, methanol was removed under a reduced pressure to produce a glassy solid that was dried in vacuum for 5 h to afford the title compound 11 (41.4 mg, 0.232 mmol) in 98% yield, 15,20 …”