Expanded Scope in Ethylene−Alkyne Cross-Metathesis: Coordinating Heteroatom Functionality at the Propargylic Position
摘要:
[GRAPHICS]The Grubbs 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene-substituted ruthenium complex 1 catalyzed ethylene-alkyne cross-metathesis and was shown to tolerate free hydroxyl groups and coordinating functionality at the propargylic and homopropargylic positions, Hindered and enantiomerically enriched 1-substituted alkynes also react efficiently under the reported conditions.
Two buta-2,3-dienylstannanes, 1-tri-n-butylstannylbuta-2,3-diene and 1-triphenylstannylbuta-2,3-diene, have been prepared and shown to react with aldehydes and acetals under Lewis acid catalyzed conditions producing (buta-1,3-dien-2-yl)methanol derivatives in high yields.
examined establishing an efficient method for the preparation of alkyl(1,3-butadien-2-yl)methanols. Application of this method to chiral acetals prepared from (R,R)-2,4-pentanediol led to chiral alkyl(1,3-butadien-2-yl)methanol derivatives with high optical purity which were alternatively synthesized by the Sharpless kinetic resolution of racemic alkyl(1,3-butadien-2-yl)methanols.
Diels–Alderreactions of ten 2-substituted buta-1,3-dienes 1a–j with N-phenylmaleimide were examined under various conditions, demonstrating that an allylic heteroatom substiuent at the C-2 position exerts significant directing effect on diastereofacial selection and also that the diastereofacial selectivity can be enhanced by use of 5 mol dm–3 LiClO4–Et2O as a reaction medium.