Electron-transfer-induced photochemical reactions of (silylallyl)iminium and benzylpyrrolinium salts by dual diradical and diradical cation cyclization pathways

Two Interrelated Strategies for Cephalotaxine Synthesis

“…To briefly assess the mechanistic pathway(s) operating in the photocyclization reaction, tetradeuterioiminium salt 13D 4 was prepared and subjected to direct irradia- The dominance (ca. 8:1) of cation diradical cyclization in this mechanism as compared to that operating for nonaryl analogs 22 (ca. 1:1) is not easily rationalized.…”

“…Further investigations demonstrated that a dual mechanistic sequence ( i.e. , diradical and diradical cation coupling) was responsible for carbon−carbon bond formation in this process and that the scope of the photocyclization reaction was narrow when α-aryl-substituted iminium salts were used. 21b, In spite of these issues, the high efficiency of the spirocyclic amine forming sequence exemplified by the transformations IV → V → VI suggested that it might serve as the basis for a new strategy for cephalotaxus alkaloid synthesis. As depicted in Scheme , a cephalotaxine synthetic route based on this design relies on photocyclization of a silylallyliminium salt ( IX ) which itself derives from a β-enaminone precursor X .…”

“…20 At that time, we also discovered that tethered allylsilaneiminium salts related to V could be readily prepared from β-enamino ketone precursors IV and that these substances undergo SET-promoted photocylization to produce spirocyclic amine products (e.g., VI). 21 Further investigations demonstrated that a dual mechanistic sequence (i.e., diradical and diradical cation cou-pling) was responsible for carbon-carbon bond formation in this process 22 and that the scope of the photocyclization reaction was narrow when R-aryl-substituted iminium salts were used. 21b,23 In spite of these issues, the high efficiency of the spirocyclic amine forming sequence exemplified by the transformations IV f V f VI suggested that it might serve as the basis for a new strategy for cephalotaxus alkaloid synthesis.…”

Conversion of Aryl Aldehydes to Benzyl Iodides and Diarylmethanes by H3PO3/I2

“…This compound is known. 22 1-(tert-Butyl)-4-(iodomethyl)benzene (2e). Light yellow oil, yield 82%, 134.9 mg; Eluent: Petroleum ether/EtOAc = 40/1.…”

Succinct Syntheses of Methopholine, (±)‐Homolaudanosine, and (±)‐Dysoxyline via Metal‐free One‐Pot Double Alkylation on 1‐Methyl‐3,4‐dihydroisoquinolines

“…In case of the iminium salt of DHIQ, at first the iminium needed to be converted to enamine in the presence of bases, and subsequent alkylation 31 or acylation 32 were facilitated. Allylation at the C1‐methyl of DHIQ was accomplished using allyl iodide and a strong base, such as n ‐butyllithium . Lately, we also reported a novel approach for the C1‐methyl alkylation on DHIQ‐enamides using Grignard reagents .…”