An efficient and step-economic new approach to alkyl citrate natural products from a cyclobutene diester is presented. The key sequence involves a formal [2 + 2]-cycloaddition of a silylketene acetal with dimethylacetylene dicarboxylate to provide the cyclobutene diester 14 with 4.5:1 stereoselectivity. Exposure of diester 14 in acidic methanol effected a hydrolysis, intramolecular oxy-Michael reaction, and cyclobutanone methanolysis cascade to give the triester 15. Iodination and elimination then afforded a key alkyl citrate alkene intermediate, which was converted into the natural products (-)-CJ-13,982 (1), (-)-CJ-13,981 (2), and (-)-L-731,120 (3) via a cross-metathesis and subsequent reduction.

EH9 3JJReaction of aniline with pentyl nitrite and acetic anhydride in benzene, or other solvents, gives benzyne in up to 32% yield as measured by trapping with anthracene, and tetraphenylcyclopentadienone and its 2.5-di-p-tolyl analogue. The role of the anhydride is to by-pass the suppressive effect of water on benzyne formation from the diazonium acetate ion pair. Reaction in benzene of aniline-acetic anhydride or (better) acetanilide with p-chlorobenzoyl nitrite (PCBN) (from silver p-chlorobenzoate and nitrosyl chloride) gives benzyne in up to 71% yield as measured by trapping as before and by 9.1 O-dimethoxyanthracene, and by the ene reaction with methyl methacrylate to give ethyl 2-methylene-3-phenylpropionate (31 %). m e w Substituted anilines and acetanilides (m-XCGHQ*-NHAc; X = F. CI, Br, I, CO,Et, MeO, But, CFs, or NO2) and 3-aminopyridine behave like aniline and acetanilide. the para-isomers give lower yields, and the ortho-isomers give little or no arynes. with the exception of ethyl anthranilate and 2.5-dimethoxy-and 2.5-dichloroaniline.

Two cis-β-MnIIISALPN catalysts were synthesised and tested in the Mukaiyama–Isayama hydration of α,β-unsaturated esters.

The stereoselective 12-step total synthesis of the reassigned structure for citrafungin A (1a) via cyclobutene diester 10 is described. Key steps involved a formal [2 + 2]-cycloaddition, oxa-Michael/cyclobutanone ring-opening cascade to secure the alkyl citrate core, and asymmetric vinylzinc addition to form the C6 stereocenter. In addition, no oxidative adjustments are required to secure the citrate oxidation level.