Intramolecular Allylsilane Addition to Chiral Alkylidene‐1,3‐dicarbonyl Compounds for the Synthesis of Enantiomerically Pure trans‐1,2‐Disubstituted Cyclopentanes and Cyclohexanes

Abstract

Three new stereogenic centers characterize the 1,2‐trans‐disubstituted cyclopentanes 2a and cyclohexanes 2b, which can be prepared enantiomerically pure with the Lewis acid SnCl4 in a highly selective SnCl4‐induced cyclization of the chiral alkylidene malonic acid derivatives 1a and 1b, respectively. The chiral auxiliary can be removed from 2 with LiAlH4.

New Lewis-Acidic Molybdenum(II) and Tungsten(II) Catalysts for Intramolecular Carbonyl Ene and Prins Reactions. Reversal of the Stereoselectivity of Cyclization of Citronellal

“…The synthesis of ( E )- and ( Z )-allylsilanes 9 and 10 commenced with the protected hydroxy aldehyde 13 , available in two steps from 1,6-hexanediol (Scheme ). Wittig olefination of 13 with Ph 3 PCHCO 2 Et (80 °C, 3 h) afforded the α,β-unsaturated ester 14 (89%; E / Z = 96:4), whose reduction with diisobutylaluminum hydride in toluene (−20 °C, 25 min) furnished allylic alcohol 15 (90%). 24a,b, Acetate 16 , obtained from the latter alcohol (Ac 2 O, pyridine, rt, overnight; 93%), was treated with (PhMe 2 Si) 2 CuLi (THF, −60 °C, 12 h) to give allylsilane 17 (67%). − Deprotection of the latter product ( 17 → 18 ; p -TsOH, MeOH, rt, 7 h; 89%), followed by Collins oxidation, afforded the required aldehyde 9 (59%). Similar strategy was applied to the synthesis of the ( Z )-isomer 10 : aldehyde 13 5b was converted in two steps into the propargylic derivative 19 (81%), whose hydrogenation on Lindlar catalyst gave ( Z )-ester 20 (99%).…”

Stereochemical Control in Organic Synthesis Using Silicon-Containing Compounds

“…The product structure can have an influence, with the formation of the triquinane 1214 from the allylsilane 1213 being the result of a natural preference for both ring fusions to be cis (Scheme ) ) 299 …”

A Base-Catalyzed, Domino Aldol/hetero-Diels–Alder Synthesis of Tricyclic Pyrano[3,4-c]chromenes in Glycerol

“…A highly atom economic, efficient, and environmentally friendly method has been the prime synthetic target to be achieved by chemists for synthesizing complex heterocycles over the last few decades . Domino strategies in this context seem to have been widely explored by coupling Knoevenagel transformation with hetero -Diels–Alder, ene, allylsilane cyclization, and 1,3-dipolar cycloaddition reactions in the development of cascade synthetic routes for the synthesis of a diverse range of bioactive fused-ring systems. In the same way, imine generation coupled with hetero -Diels–Alder transformation happens to be an interesting example of a growing research area in synthetic organic chemistry.…”