Synthesis of enantioenriched homopropargylic alcohols through diastereoselective SE' additions of chiral allenylstannanes to aldehydes
摘要:
Allenylstannanes (S)-4 and (R)-4, available in ca. 90% ee from alkynones 1 through reduction with the LiAlH4-Darvon alcohol or -ent-Darvon alcohol complex, followed by S(N)2' displacement on the derived mesylates (R)-3 or (S)-3 with Bu3SnLi.CuBr.Me2S, readily add to various aldehydes under Lewis acid catalysis to afford optically active homopropargylic alcohols with good to excellent syn diastereoselectivity. With 2-(benzyloxy)propanal (48), MgBr2-catalyzed reactions are highly stereoselective, affording the syn adduct 49 from the (S)-stannane (S)-4 and the anti adduct 52 from the (R)-stannane (R)-4. BF3-promoted additions give mainly or exclusively the syn adducts 49 and 51. Additions of (S)- and (R)-4 to (R)-3-(benzyloxy)-2-methylpropanal (61) yield the syn adducts 62 and 64 as major or exclusive products.
Lepadiformine A、B 和 C 是使用还原环化策略以对映体纯形式合成的。N -Boc α-氨基腈被去质子化并用对映体纯二溴化物烷基化以提供第一个环。操纵产物以引入磷酸盐离去基团,随后的还原锂化和分子内烷基化形成具有高立体选择性的第二个环。第三个环是通过去保护的胺分子内置换甲磺酸盐形成的。Lepadiformine A 和 B 含有一个与胺相邻的羟甲基。使用 Polonovski-Potier 反应作为关键步骤,按顺序引入该附属物。合成策略具有立体选择性和收敛性,并证明了N的效用-Boc α-氨基腈作为生物碱合成的关键。
We report the high reactivity of electron-deficient enynes in the homo-benzannulation of conjugatedenynes in the presence of Pd(PPh3)4. The introduction of electron-withdrawing groups enabled us to carry out the benzannulation of 1-substituted enynes as well as 1,2- and 2,4-disubstituted enynes. Polysubstituted benzenes were prepared in a highly regioselective manner in good to excellent yields.
A directC(sp2)H alkynylation of aldehyde C(O)H bonds with hypervalent iodine alkynylation reagents provides ynones under metal‐free conditions. In this method, 1‐[(triisopropylsilyl)ethynyl]‐1,2‐benziodoxol‐3(1H)‐one (TIPS‐EBX) constitutes an efficient alkynylation reagent for the introduction of the triple bond. The substrate scope is extended to a variety of (hetero)aromatic, aliphatic, and α
Investigation of the Cyclopentenone Formationvia the ?-Alkynone Cyclisation: Synthesis of the Acorone Intermediate 8-Methylspiro[4.5]deca-3,7-dien-2-one
作者:John Ackroyd、Martin Karpf、Andr� S. Dreiding
DOI:10.1002/hlca.19850680208
日期:1985.3.27
of the cyclopentenone formation ACvia the thermal α-alkynone cyclisation BC and in order to test the fate of an isolated C,C-double bond within a molecule under these conditions, we investigated the synthesis of the acorone intermediate 3starting from the known carboxylic acid 1. The α-alkynone 2 was obtained from 1via the acyl chloride 6 and a Pd(II)-catalysed route (22%). The thermolysis of 2 at
Allyl-aryl coupling between allylic acetates and arylboronicacids took place in the presence of catalytic amounts of Pd(OAc)(2), 1,10-phenanthroline, and AgSbF(6) with high gamma-selectivity and E/Z-selectivity. The reaction of an optically active allylic acetates with an alpha-stereogenic center proceeded with excellent alpha-to-gamma chirality transfer with syn-selectivity and gave the corresponding
meso-Phbox-Pd(ii) catalyzed tandem carbonylative cyclization of 1-ethynyl-1-propargyl acetate
作者:Keisuke Kato、Ryuhei Teraguchi、Satoshi Motodate、Akira Uchida、Tomoyuki Mochida、Tat’yana A. Peganova、Nikolai V. Vologdin、Hiroyuki Akita
DOI:10.1039/b806207b
日期:——
Palladium(II) catalyzed carbonylation of 1-ethynyl-1-propargyl acetate 1 is described; in the absence of the bisoxazoline (box) ligand, the second triple bond did not react, affording cyclic orthoesters 3 and 4. The use of meso-Phbox-Pd(II) strikingly changed the course of the reaction, yielding bicyclic lactone 2 by tandem carbonylative cyclization as a result of insertion of the second triple bond.