Brominative Deoxygenation of some aldehydes and ethers

Abstract

Three aldehydes (4a–c) are transformed into 1,1‐dibromides (6a–c) by 2,2,2‐tribromo‐2,2‐dihydro‐1,3,2‐benzodioxaphosphole (2). This reagent (2) is also very active in the cleavage of ethers; its reactions may show some features of carbonium as well as of SN2 character.

Shorter and Easier Syntheses of Di‐tert‐butylketene and Relatedgem‐Di‐tert‐butyl Compounds

“…The aldehyde 8 is almost instantaneously deoxygenated by the catechyl phosphorus tribromide 64 (Scheme ), which is approved48 for the preparation of 1,1‐dibromides such as the desired t Bu 2 CH–CHBr 2 . However, the repulsive strain inherent in the gem ‐ t Bu 2 fragment appears to lead 8 away from the intended course, producing instead the de‐ tert ‐butylated alkenyl bromide 65 as the pure ( Z ) isomer,49 which was slowly converted into the ( E ) isomer 66 under the reaction conditions.…”

“…1‐Bromo‐3,3‐dimethylbut‐1‐ene (65 and 66): The reaction between the aldehyde 8 (50 mg, 0.32 mmol) and 2,2,2‐tribromo‐2,2‐dihydrobenzo‐1,3,2‐dioxaphosphole ( 64 , 1.60 mmol)48 in 1,2‐dichloroethane (0.5 mL) was complete within <5 min at room temp., as shown by in situ 1 H NMR spectroscopy, which also revealed the formation of t BuBr ( δ H = 1.78 ppm) and exclusively the ( Z ) isomer 65 . 1 H NMR (ClCH 2 CH 2 Cl): δ = 1.24 (s, 3 × CH 3 ), 6.02 and 6.16 (AB system with 3 J = 8 Hz, 1‐/2‐H) ppm 49.…”