Reactions of diphenylcarbene with alkenes, alkynes, and alkenynes

Abstract

Diphenylcarbene reacts with olefins by both addition and abstraction. The partitioning of the reaction between these paths is determined largely by steric factors. The stereochemistry of addition has been determined in a system favorable to triplet reaction. With acetylenes, both addition and abstraction occur, but the intermediate generated by addition is often diverted from a path leading to the usual cyclopropene and gives indene instead.

Polylithiumorganic compounds. Part 29: C,C Bond cleavage of phenyl substituted and strained carbocycles using lithium metal

“…1 H NMR data were in accordance with literature values. 35 The same reaction was performed starting with 0.60 g (4.6 mmol) of 26 and 0.20 g (30 mmol) of lithium, quenching was performed after filtration with 2.0 mL (45 mmol) of methanol-d 1 at K90 8C. After bulb-to-bulb condensation 0.30 g (50%) were obtained, the main product was purified by preparative gas chromatography.…”

Orbital preferences in generation of singlet arylcarbenes

“…Conformational effects may be expected to influence the properties of 2 as singlets, especially in light of evidence indicating the importance of phenyl twisting on the chemistry of triplet diphenylcarbene. 6 Of note is that para-monosubstituted diphenylcarbenes add preferentially to cyclopentadiene to give 6,6-diphenylbicyclo[3.1.0]hex-2-enes in which the more electron rich aryl group is endo (7, Z = CH3, OCH3; 8, Z = Br, CN) to the cyclopentene ring.7 The selectivity has been rationalized in terms of a singlet-like transition state in which the aryl rings of the carbene are essentially coplanar and the only significant substituent effect is interaction with the ini- Journal of the American Chemical Society / 99:3 / February dally vacant p orbital of the carbene.7 It now appears that inclusion of large substituent-generated steric effects offers an alternative explanation of these observations. That is, when Z is electron withdrawing, the substituted aryl function aligns to maximize the overlap with the electron rich -orbital of the carbene.…”

“…In all cases [PDBA] was in the range (5.2-5.4) X 10-3 molar residue. [PDBA] = 4.8 X 10-3 molar residue [Cu(ll)] = 1.2 X 10~3 : (1) pH 8.29, (2) pH 9.31, (3) pH 10.18,(4) pH 11.67, (5) pH 12.09, (6) pH >13.…”

“…Calculated Equilibrium Geometries(5,6) and Heats of Formation of Singlet Para-Substituted Phenylcarbenes(3) …”

2-Biphenylenylcarbene1

“…Naturally, phenylcarbene was the first species explored, and it was quickly determined that although the ground state was the triplet, much of its chemistry issued from the slightly higher energy (but much more reactive) singlet state . However, phenyl diazomethane is hard to handle, and many workers chose to study 1- and 2-naphthylcarbene, fluorenylidene, and diphenylcarbene, all available from more tractable precursors. In these two-ring carbenes 4-6 the ground state is again the triplet, but once more, much of the observed chemistry is derived from reactions of the singlet.…”