Nitrones-III

Synthesis of optically active nicotinoids

“…Shioiri reported a yield of 81% and an [a]20D -70.7°(c 1.0, methanol). The specific rotation of 4 is substantially greater than that obtained by our process: [a]20D -32.5°( c 2.57, methanol). Shioiri has stated that the preparation of 4 "proceeds without loss of optical activity".…”

“…We also addressed the possibility of partial racemization during the condensation step, e.g., 4 to 19. It is conceivable that the anion of 4 could potentially induce ring opening through ß elimination of the amino moiety to afford an open-chain e-amino-a,/3-unsaturated nitrile.…”

Pyrrolo[2,1-a]isoquinolines (review)

“…In the opinion of the authors of [133], azomethine ylides of the (LIX) type, generated from 1,2,3,4-tetrahydroisoquinoline and diarylideneacetone, undergo 1,5-electrocyclization followed by prototropic rearrangement with the formation of compounds ( A similar result was obtained with unsaturated carboxylic acids [135], ethyl propiolate [136], 1,2-di(trifluoromethyl)acetylene [137], and phospholipids [138] as dipolarophiles. In the last case, the reaction takes place through the formation of the aziridines (LXV).…”

Lactones 38: Synthesis and odoriferous properties of p‐menthane lactones

“…Since stereochemistry of the Horner-Wadsworth-Emmons reaction strongly depends on applied conditions, especially temperature, solvent and structure of phosphonate used for olefination, we made some attempts with different phosphonates and bases to obtain esters with cis configuration of the a,b-situated double bond. [48][49][50][51][52] The olefination of isopulegone 10a or 10b with methyl P,P-bis(2,2,2-trifluoroethyl)phosphonoacetate, potassium bis-(trimethylsilyl)amide (KHMDS) and 18-crown-6 or ethyl diphenylphosphonoacetate and benzyltrimethylammonium hydroxide afforded only small amounts of ethyl or methyl esters with trans configuration of the a,b-situated double bond. In addition, the trans isomers low-yield formation was also favoured at temperatures below room temperature, whereas at minus temperatures no products of the olefination were formed.…”