Pentacarbonyl (η²-cis-cyclo-octene)chromium: photochemical synthesis of a useful Cr(CO)₅transfer reagent

Synthesis and Structure of 2-Hydro-, 2-Alkyl-, 2-Alkynyl-, and 2-Stannyl-2,3-dihydro-1H-1,3,2-diazaboroles

“…(14)ϪO (14) 177.9(6) C(2)ϪN(2)ϪC(11) 122.1 (2), N(2)ϪC (2) [8] [(Z)-cyclooctene]Cr(CO) 5 . [21] LiAlH 4 …”

Highly Regio‐ and Diastereoselective Chromium(0)‐Catalysed Cyclopropanation of 1‐Alkoxy‐1,3‐dienes with Diazo Compounds

“…1-Alkoxy-1,3-butadienes 4Ϫ8 applied to cyclopropanation A solution of 9-diazo-9H-fluorene (2) [10] in dichloromethane was added at room temp. over a period of 8 h to a solution of 1-alkoxy-1,3-butadiene (molar ratio 2/diene ϭ 1:1) and 2 mol % pentacarbonyl(η 2 -cis-cyclooctene)chromium(0) (1) [11] in dichloromethane, and the reaction mixture was stirred for a further 8 h. The spiro-vinylcyclopropanes 9Ϫ13 were obtained in 51Ϫ97% yield after chromatographic work-up (Scheme 2, Table 1 The less electron-rich aryl-substituted 1,3-butadienes (e.g. 1-phenyl-1,3-butadiene and 1,4-diphenyl-1,3-butadiene) and 1-acetoxy-1,3-butadiene did not produce the desired cyclopropanation products under these conditions.…”

Chromium Complex Catalyzed Synthesis of Spirocyclopropanes from Diaryl Diazo Compounds – Direct NMR-Spectroscopic Observation of a Carbene Complex Intermediate

“…Cyclopropanations with 9-Diazo-9H-fluorene (1): Addition of a solution of 9-diazo-9H-fluorene (1) [9] in dichloromethane to a solution of the respective electron-rich olefin (molar ratio 1/alkene ϭ 1:1) and 2 mol% pentacarbonyl(η 2 -ciscyclooctene)chromium(0) (2) [10] in dichloromethane over a period of 8 h, followed by stirring for a further 8 h, gave spirocyclopropanes 3Ϫ7 in 15Ϫ93% yield after chromatographic work-up (Scheme 1, Table 1). Scheme 1.…”

“…Liquid starting compounds were degassed under vacuum and stored over molecular sieves (4 Å ). Compounds 1, [9] 2, [10] 13, [16] 17, [18] 18, [19] 20, [16] 22Ϫ25, [26] [27] [28] [29] 2-vinyloxyethyl acrylate [17] and (Z)-propenyl benzyl ether [24] were prepared according to published procedures. All other chemicals were used as received from commercial sources.…”