P(PhCH_2NCH_2CH_2)_3N: An Efficient Lewis Base Catalyst for the Synthesis of Propargylic Alcohols and Morita_Baylis_Hillman Adducts via Aldehyde Alkynylation

摘要

Proazaphosphatrane P(PhCH_2NCH_2CH_2)_3N (1a) is an efficient catalyst for the addition of aryl trimethylsilyl alkynes to a variety of aromatic, aliphatic, and heterocyclic aldehydes in THE at room temperature. The reaction conditions are mild and employ a low catalyst loading (ca. 5 mol %). Only propargylic alcohols were isolated in good to excellent isolated yields when electron-rich, electron-neutral, heterocyclic, and aliphatic aldehydes were employed, whereas β-branched Morita_Baylis_Hillman (MBH) type adducts were isolated with electron-deficient aromatic aldehydes after conventional acid hydrolysis of the TMS ether products. Alkynes containing heterocyclic and aromatic groups bearing electron-withdrawing or -donating substituents underwent clean addition to cyclohexanecarboxaldehyde and to electron-rich aromatic aldehydes to give propargylic alcohols in excellent isolated yields. β-Branched Morita_Baylis_Hillman (MBH) type adducts were isolated when electron-deficient aromatic aldehydes were employed. Reaction pathways to both types osf products are proposed.