title: Highly stereoselective synthesis of anti,anti-dipropionate stereotriads: a solution to the long-standing problem of challenging mismatched double asymmetric crotylboration reactions.
abstract: The stereocontrolled synthesis of the β-branched anti,anti-dipropionate stereotriad 4 via aldol or crotylmetal chemistry represents a historical challenge to the organic synthesis community. Here we describe a general solution to the long-standing problem associated with the synthesis of 4 by utilizing mismatched double asymmetric crotylboration reactions of enantioenriched α-methyl substituted aldehydes with the chiral, nonracemic crotylborane reagent (S)-(E)-22 (or its enantiomer). This method not only provides direct access to anti,anti-dipropionate stereotriads 24 [a synthetic equivalent of 4] with very good (5-8:1) if not excellent (≥15:1) diastereoselectivity from β-branched chiral aldehydes with ≤50:1 intrinsic diastereofacial selectivity preferences but also provides a vinylstannane unit in the products that is properly functionalized for use in subsequent C-C bond-forming events. We anticipate that this method will be widely applicable and will lead to substantial simplification of strategies for synthesis of polyketide natural products.
authors.affiliation: Department of Chemistry, Scripps Florida, Jupiter, Florida 33458, USA.
authors.forename: Ming
authors.initials: M
authors.lastname: Chen
authors.forename: William R
authors.initials: WR
authors.lastname: Roush
mesh_terms: D000447:Aldehydes / Q000737:chemistry; D001880:Boranes / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D009947:Organotin Compounds / Q000737:chemistry; D061065:Polyketides / Q000138:chemical synthesis* / Q000737:chemistry; D011422:Propionates / Q000138:chemical synthesis* / Q000737:chemistry; D012996:Solutions; D013237:Stereoisomerism
chemical_list: D000447:Aldehydes; D001880:Boranes; D009947:Organotin Compounds; D061065:Polyketides; D011422:Propionates; D012996:Solutions