title: Ruthenium Catalyzed Diastereo- and Enantioselective Coupling of Propargyl Ethers with Alcohols: Siloxy-Crotylation via Hydride Shift Enabled Conversion of Alkynes to π-Allyls.
abstract: The first enantioselective carbonyl crotylations through direct use of alkynes as chiral allylmetal equivalents are described. Chiral ruthenium(II) complexes modified by Josiphos (SL-J009-1) catalyze the C-C coupling of TIPS-protected propargyl ether 1a with primary alcohols 2a-2o to form products of carbonyl siloxy-crotylation 3a-3o, which upon silyl deprotection-reduction deliver 1,4-diols 5a-5o with excellent control of regio-, anti-diastereo-, and enantioselectivity. Structurally related propargyl ethers 1b and 1c bearing ethyl- and phenyl-substituents engage in diastereo- and enantioselective coupling, as illustrated in the formation of adducts 5p and 5q, respectively. Selective mono-tosylation of diols 5a, 5c, 5e, 5f, 5k, and 5m is accompanied by spontaneous cyclization to deliver the trans-2,3-disubstituted furans 6a, 6c, 6e, 6f, 6k, and 6m, respectively. Primary alcohols 2a, 2l, and 2p were converted to the siloxy-crotylation products 3a, 3l, and 3p, which upon silyl deprotection-lactol oxidation were transformed to the trans-4,5-disubstituted γ-butyrolactones 7a, 7l, and 7p. The formation of 7p represents a total synthesis of (+)-trans-whisky lactone. Unlike closely related ruthenium catalyzed alkyne-alcohol C-C couplings, deuterium labeling studies provide clear evidence of a novel 1,2-hydride shift mechanism that converts metal-bound alkynes to π-allyls in the absence of intervening allenes.
authors.affiliation: Department of Chemistry, University of Texas at Austin , 1 University Station, Welch Hall A5300, Austin, Texas 78712, United States.
authors.forename: Tao
authors.initials: T
authors.lastname: Liang
authors.affiliation: Department of Chemistry, University of Texas at Austin , 1 University Station, Welch Hall A5300, Austin, Texas 78712, United States.
authors.forename: Wandi
authors.initials: W
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, University of Texas at Austin , 1 University Station, Welch Hall A5300, Austin, Texas 78712, United States.
authors.forename: Te-Yu
authors.initials: TY
authors.lastname: Chen
authors.affiliation: Department of Chemistry, University of Texas at Austin , 1 University Station, Welch Hall A5300, Austin, Texas 78712, United States.
authors.forename: Khoa D
authors.initials: KD
authors.lastname: Nguyen
authors.affiliation: Department of Chemistry, University of Texas at Austin , 1 University Station, Welch Hall A5300, Austin, Texas 78712, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Krische
mesh_terms: D000438:Alcohols / Q000737:chemistry*; D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D004987:Ethers / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D012833:Siloxanes / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000438:Alcohols; D000480:Alkynes; D004987:Ethers; D012833:Siloxanes; C531209:propargyl ether; D012428:Ruthenium