(E)-Selective olefination of aldehydes by means of gem-dichromium reagents derived by reduction of gem-diiodoalkanes with chromium(II) chloride

The first total synthesis of (+)-mucosin

“…Despite the low 70 recovery this method provided further evidence for the relative stereochemistry of the major diastereoisomer given that alcohol 19a cannot undergo iodoetherification, and some evidence that the minor isomer is 19b which can. Oxidation of the alcohol 19a to aldehyde 20 followed by Takai olefination 18 with diiodide 21 and removal of the silicon protecting group with TBAF gave the alcohol 23 in 81% overall 10 yield. Finally alcohol 23 was oxidised to mucosin 1 in 84% yield using PDC in DMF (Scheme 4).…”

Lombardo’s Reagent

“…It converts ketones into methylene groups. 1 The active reagent is presumed to be a dimetalated species (1) which adds to the ketone under the influence of the Lewis acidity of titanium to give a b-oxymetal-substituted organometallic compound (2). Following b-elimination generates the methylene group (3) 2 (Scheme 1).…”

Trace Amounts of Second Metal Elements Can Play a Key Role in the Generation of Organometallic Compounds

“…The gemdiiodoalkane-chromium(II) chloride-DMF method provides alkylidenation products with a high level of E-selectivity, especially when applied to aliphatic aldehydes (Scheme 25). 49 Because the olefination proceeds under mild conditions, functional groups such as ester, nitrile, 1,3-diene, acetylene, olefin, epoxide, alkyl bromide, and acetal are also tolerated during the reaction.…”

“…In contrast to zinc, the second reduction of gem-diiodoalkane with chromium(II) proceeds relatively well to give gem-dichromium species, and a carbon connected to chromium(III) has sufficient nucleophilicity toward aldehydes (Scheme 31). 49 …”