Conformational analysis of substituted hexahydropyrrolo [2,3-b]indoles and related systems. An unusual example of hindered rotation about sulfonamide SN bonds. An X-ray crystallographic and NMR study

Structure, modelling and dynamic behaviour of aza- and azaoxamacrocyclic ligands derived from (R,R)-1,2-diaminocyclohexaneElectronic supplementary information (ESI) available: different views of compounds 6, 6a and 6b. See http://www.rsc.org/suppdata/ob/b3/b306963j/

“…The Arrhenius and Eyring plots were both linear, and gave E a = 37.2 kJ mol Ϫ1 and Arrhenius A-factor = 5.7 × 10 10 , and ∆H* = 65.8 kJ mol Ϫ1 and ∆S* = 94.3 J K Ϫ1 mol Ϫ1 respectively. The free energy of activation (∆G*) for N-inversion or N-S bond rotation of a tosyl derivative was determined to be 57.3 kJ mol Ϫ1 at 273 K. 9 The Eyring parameters derived above for the lower temperature dynamic process predict a value for the N-S bond free energy rotation barrier at 273 K, ∆G* = 40.1 kJ mol Ϫ1 , which is of a similar magnitude to that reported. 9 Analysis of the lower frequency, methyl group region of the temperature dependent 1 H-NMR spectra of 6 revealed that at lower temperatures there are two equally intense methyl singlets, which coalesce around 290 K, collapsing to a single signal at higher temperatures, Fig.…”

On the prevalence of bridged macrocyclic pyrroloindolines formed in regiodivergent alkylations of tryptophan

“…pro- S addition at C3). 19 Though a discrete exo diastereomer has not been observed, the latter possibility is supported by the near equal ratio of C3- to C2-linked products in the aforementioned seven examples. In two additional acid-promoted cyclizations, however, indole C2-linked macrocycles were obtained in the absence of pyrroloindoline products (see ESI Fig.…”

“…This finding is consistent with reported thermodynamic preferences of related pyrroloindolines. 3b , 4e , 19 Preference for the endo -pyrroloindoline in this case is primarily due to 1,3-allylic strain resulting from the tertiary amide (ESI Fig. S15 † ).…”

Stereocontrolled and Versatile Total Synthesis of Bispyrrolidinoindoline Diketopiperazine Alkaloids: Structural Revision of the Fungal Isolate (+)‐Asperdimin

“…To set the right configuration at C2/C2', we took full advantage of the thermodynamic preference of exo-2-acyl hexahydropyrroloA C H T U N G T R E N N U N G [2,3-b]indoles to place the acyl group at the endo position under basic equilibrating conditions. [11] This striking bias for the endo isomer, which has been attributed to torsional interactions around the bicycloA C H T U N G T R E N N U N G [3.3.0]octane nucleus, [18] provided a significant flexibility to our methodology. Thus, treatment of the exo dimer 16 a with 4 equivalents of lithium bis(trimethylsilyl)amide (LiHMDS) at À15 8C in THF, followed by quenching of the corresponding lithium enolates with MeOH at À78 8C, afforded the diastereomeric endo dimer 25 in almost quantitative yield (Scheme 7).…”