The use of silicon-based tethers for the Pauson-Khand reaction

Abstract

A range of silicon-based tethers and promoters have been investigated for use in the development of a silyl-tethered Pauson-Khand reaction.

Dicyanamide Salts that Adopt Smectic, Columnar, or Bicontinuous Cubic Liquid‐Crystalline Mesophases

“…Thus,t he breakdown of the ionic sublayersi nt he SmA phases of 1 and 2 (which feature the same alkyl chain volumep er molecule) resultsi nc learing to the isotropic liquid state and is governed by the temperature-dependent molecular cross-sectional area. [1,42,48,50] The calculated values of A M,limit are larger than those reported for 1-[3,4-bis(hexyloxy)benzyl]-3methylimidazolium halides (ca. 52.5 2 ) [48] and 1-(4-dodecyloxy-benzyl)-3-methylimidazolium salts (ca.…”

“…ment with ab ilayer structure:f or N = 2a t9 2 8C: A M % 55.6 2 for 1 and A M % 59.8 2 for 2.A tt his temperature, the cross-sectional area of one fully stretched aliphatic chain, s ch ,e quals about 22.4 2 , [39] whichi ndicates that the two molten alkyl chains that are connected to each cation are folded (andpossibly partially interdigitated with chains from the neighboring smecticl ayer) in the aliphatic sublayers. [40][41][42][43] The slightly larger A M value that was calculated for 2 is consistent with its more voluminous cationic headgroup as compared with 1 (i.e., ÀN + (C 2 H 5 ) 3 versus ÀN + (CH 3 ) 3 ). Larger ionic headgroupst ypically result in smaller smecticl ayer spacings due to increased chain foldinga nd interdigitation to achieve ab alance between the area of the cationic headgroup/anion assembly that is projected onto the smecticl ayer planesa nd the cross-sectional area(s)o ft he respective alkyl chain(s) attachedt ot he cation.…”

“…Larger ionic headgroupst ypically result in smaller smecticl ayer spacings due to increased chain foldinga nd interdigitation to achieve ab alance between the area of the cationic headgroup/anion assembly that is projected onto the smecticl ayer planesa nd the cross-sectional area(s)o ft he respective alkyl chain(s) attachedt ot he cation. [42,[44][45][46][47][48] In this case, however, d was found to be similar for the SmA phases adopted by 1 and 2 (Table 2a nd Figure 7a). This result suggested to us that the bulkier ÀN + (C 2 H 5 ) 3 headgroups may cause the ionic sublayerst oe xpand in lateral as well as longitudinal directions due to "rippling" or "undulation" (Figure 6a).…”

Five‐Membered Carbocycles

“…Dobbs has explored the use of silyl ether, silyl acetal, and silyl alkyl tethers in the PKR. 51 Under his conditions, only sily ethers produced cyclopentenones. The best results required two isopropyl groups on the silicon.…”

“…The improved yields observed with intramolecular versus intermolecular PKRs have encouraged attempts to facilitate the reaction with a cleavable tether that contains ether or silyl groups. 46 " 51 The intramolecular PKR has seen the most application for synthesis. There are numerous examples of the formation of carbocyclic and heterocyclic systems.…”