Reduction of acrolein dialkyl, acetals with CrCl2. γy-alkoxy substitued allylic chromium reagents for selective synthesis of erythro-1, 2-diols.

Carbon−Carbon Bond Formations Involving Organochromium(III) Reagents

“…[92][93][94] Vinylepoxides also react with Cr(II) in the presence of LiI to afford functionalized allylic chromium reagents, 95 as do acrolein dialkyl acetals in the presence of Me 3 SiI. 96 The reactivity of these functionalized species is discussed in section VI B. Attempted conversions of allyl sulfones into the corresponding organochromium reagents on exposure to Cr(II), however, met only with limited success.…”

Chromium‐Catalyzed Pinacol‐Type Cross‐Coupling: Studies on Stereoselectivity

“…The reactions were catalyzed by chromium chloride with stoichiometric amounts of manganese as reducing agent, by a protocol originally developed by Fürstner for a catalytic NozakiHiyama reaction. [9,10] In this catalytic version of a method reported by Takai, [11] only acrolein or methacrolein acetals could be coupled to provide the corresponding pinacol monoethers, so the scope of this reaction is limited. Recently Takai reported pinacol-type cross-coupling reactions between a number of vinyl ketones and aldehydes through the use of a large excess of chromium chloride and chlorotrimethylsilane as a scavenger.…”

Structures and Total Syntheses of the Plecomacrolides

“…The chiral hydroxy ester (S)-(+)-31 was converted into the chiral aldehyde 32 via the protection, reduction, and oxidation procedure reported by Terashima [45]. Reaction of 32 with the Takai's (γ -methoxyallyl)chromium reagent [46], prepared in situ from CrCl 2 and acrolein dimethyl acetal in the presence of trimethylsilyl iodide in THF at -42 °C, produced the homoallylic alcohol, which was then converted into 33 by Scheme 4 illustrates the preparation of the C12-C17 fragment 35 starting from methyl (S)-(+)-3-hydroxy-2- The known ethyl ketone 14 [38] used in Toshima's total synthesis of bafilomycin A 1 was prepared from the sugar derivative 36 [48], obtainable from D-glucose (Scheme 5). the resultant primary alcohol was subjected to Swern oxidation to form the aldehyde, which underwent the Wittig reaction to afford the α,β-unsaturated ester 42 in 77% overall yield from the Stille coupling product.…”

“…The trans-vinylboronic acid 50 was prepared via two key asymmetric transformations, i.e. the aldehyde crotylboration [58] for assembling the C16-C17-anti stereochemistry and the Takai's (γ -methoxyallyl)chromium reagent [46] or the newly developed (γ -methoxyallenyl)stannane reagent by Roush [59] for synthesizing the C12-C15-anti-α-methoxy homoallyl/homopropargyl alcohol.…”

“…A stepwise double bond cleavage via dihydroxylation followed by glycol oxidative cleavage was carried out to convert 63 into the aldehyde 64 in 94% yield. The latter reacted with the Takai's (γ -methoxyallyl)chromium reagent [46], prepared in situ from CrCl 2 and acrolein dimethyl acetal in the presence of trimethylsilyl iodide in THF at -42 °C, to furnish 65 in good yield and in 88:12 diastereoselectivity after protection of the homoallylic alcohol as the TES ether. An alternative reagent, the Hoffmann's (E)-(γ -methoxyallyl)boronate [64], was not examined for the same transformation due to the In view of the lengthy sequence used for transforming 65 into 67 (Scheme 9) largely for protection group manipulation and for the vinyl to alkynyl conversion, Roush and coworkers revised the synthesis of the vinylboronic acid 68 as given in Scheme 10.…”