Efficient and Selective Synthesis of (S,R,R,S,R,S)-4,6,8,10,16,18-Hexamethyl- docosane via Zr-Catalyzed Asymmetric Carboalumination of Alkenes (ZACA Reaction)

Abstract

(S,R,R,S,R,S)-4,6,8,10,16,18-Hexamethyldocosane (1) was synthesized in 11% yield in 11 steps in the longest linear sequence from > or =98% pure (S)-beta-citronellal and 6 additional steps for the preparation of 11 in 23% yield from propene. Five of the six asymmetric carbon centers were generated catalytically and stereoselectively by the ZACA reaction (5 times), one lipase-catalyzed acetylation, and two chromatographic operations.

1,5-Stereocontrol in Bismuth-Mediated Reactions between Aldehydes and Allyl Bromides: Stereoselective Synthesis of Open-Chain all-syn- and anti, anti-1,3,5-Disposed Trimethylalkanes

“…16 This work has developed stereoselective syntheses of the all-syn-and anti,anti-2,4,6-trimethylnonan-1-ols 24 and 26 which should be applicable to the syntheses of analogous open-chain compounds. Although the stereoselectivities observed are somewhat less than those in other approaches to compounds of this type, [5][6][7][8] in the present work, the only chiral reagent is the initial pentenyl bromide 6, the additional stereogenic centres being introduced by 1,5-and 1,2-diastereocontrol. Indeed this chemistry could be used for a diastereoselective synthesis of racemic products.…”

“…4 We herein report an extension of this chemistry to include reactions of 5-benzyloxy-2,4-dimethylpent-2-enyl bromide (6) and the subsequent modification of the products to provide stereoselective access to openchain compounds with methyl substituents at 1,3,5-positions. This chemistry is complementary to other procedures recently introduced for the stereoselective introduction of methyl substituents along an unfunctionalised aliphatic chain which include catalyst-controlled diastereoselective hydrogenation, 5 copper-mediated allylic displacement, 6 asymmetric carboalumination, 7 and asymmetric conjugate addition. 8 Both the racemic and the R-enantiomer of (2E)-5-benzyloxy-2,4-dimethylpent-2-enyl bromide (6) were prepared from the appropriate 3-benzyloxy-2-methylpropanol (3) by oxidation using either the Swern or Dess-Martin procedure followed by an E-selective Wittig reaction to give the unsaturated ester 4.…”

“…Such structural features are found in a variety of natural products and have been the target of several recent synthetic studies. [5][6][7][8] Thus the major 1,5-anti-(2E)-product 7b from the reaction of the pentenyl bromide 6 with butanal was converted into the primary homoallylic alcohol 12 by TIPS protection followed by reductive debenzylation. The diol 13 was prepared from alcohol 7b by dissolving metal removal of the O-benzyl group, and selective TIPS protection of the primary hydroxy group of diol 13 gave the secondary alcohol 14 (Scheme 4).…”

Making Mixtures to Solve Structures: Structural Elucidation via Combinatorial Synthesis

“…Synthetic Strategy. The total or partial synthesis of polypropylene oligomers 35,36 and natural products [37][38][39][40][41][42] containing C 3 repeat units like those in the target molecules has been reported previously. While natural products might be suitable precursors to series 3, 5, and 6, they are not readily amenable to the synthesis of the other target compounds; accordingly we opted for total synthesis.…”

A Green Alternative for the Conversion of Arylboronic Acids/Esters into Phenols Promoted by a Reducing Agent, Sodium Sulfite

“…[6] However, environmentally benign transition metal-free methodologies are preferred. As alternatives, many protocols require an excess of strong oxidants such as hydrogen peroxide, [7] meta-chloroperoxybenzoic acid, [8] ammonium persulfate, [9] organic hypervalent iodine, [10] sodium chlorite, [11] N-oxides [12] or oxone®. [13] Although the synthesis of phenols from arylboronic acids has phenols using inexpensive starting materials in a simple methodology.…”