Roger W. Alder

Stable carbenes as strong bases

The stable carbene 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene has a pKa of 24 in (CD3)2SO and gives an elimination:substitution ratio with 2-bromopropane comparable to that of 1,5-diazabicyclo[4.3.0]non-5-ene (DBN).

The conformational effects of quaternary centres

Abstract Quaternary centres impose a particularly simple conformational regime on adjacent acyclic bonds; this is shown by force field calculations on alkanes and confirmed by crystal structure database studies on quaternary ammonium ions; possible implications are considered.

A 3,4‐trans‐Fused Cyclic Protecting Group Facilitates α‐Selective Catalytic Synthesis of 2‐Deoxyglycosides

A practical approach has been developed to convert glucals and rhamnals into disaccharides or glycoconjugates with high α-selectivity and yields (77–97 %) using a trans-fused cyclic 3,4-O-disiloxane protecting group and TsOH⋅H2O (1 mol %) as a catalyst. Control of the anomeric selectivity arises from conformational locking of the intermediate oxacarbenium cation. Glucals outperform rhamnals because the C6 side-chain conformation augments the selectivity.

Complexation of stable carbenes with alkali metals

Stable diaminocarbenes, including imidazol-2-ylidenes, undergo complexation with lithium, sodium and potassium species; the crystal structure of a complex of 1,3-diisopropyl-3,4,5,6-tetrahydropyrimid-2-ylidene 1 with KN(SiMe3)2 is reported.

Preparation of a range of NNN′N′-tetrasubstituted 1,8-diaminonaphthalenes

Alkylation of 1,8-bis(methylamino)naphthalene with difunctional reagents leads to a series of 1,5-dimethylnaphtho[1,8-bc]-1,5-diazacycloalkanes(1)–(5), to 1,5-dimethylbenzo[g]naphtho[1,8-bc]-1,5-diazacyclononane (6), and to 1,5-dimethylnaphtho[1,8-bc]-1,5-diaza-8-oxacyclodecane (7). A variety of attempts to develop a selective preparation of 1,8-bis(methylamino)naphthalene are reported. The preparation of 9,9-dimethylnaphtho-[1,8-bc]-1,5-diazabicyclo[3.3.1]nonane (8), naphtho-[1,8-bc]-1,5-diazabicyclo[3.2.2]nonane (9), and naphtho-[1,8-bc]-1,5-diazabicyclo[3.3.3]undecane (10) from 1,8-diaminonaphthalene are described. Reaction of appropriate 1,4- and 1,5-dihalides with 1,8-diaminonaphthalene leads to 1,8-bis-(1-pyrrolidinyl)naphthalene (11), 1,8-bis(1,3-dihydroisoindol-2-yl)naphthalene (12), 1,8-bis-(1-piperidinyl)naphthalene (13), and 1,8-dimorpholinonaphthalene (14). Nitration of 2,7-dimethylnaphthalene gives a mixture from which 2,7-dimethyl-1,8-dinitronaphthalene may be isolated; this is reduced and alkylated to give 1,8-bis(dimethylamino)-2,7-dimethylnaphthalene (15). 1,8-Bis(dimethylamino)-2,7-dimethoxynaphthalene (16) and 1,8-bis(diethylamino)-2,7-dimethoxynaphthalene (17) are similarly prepared by reduction and alkylation of 1,8-dinitro-2,7-dimethoxynaphthalene. Reaction of 2,2-dimethyl-1,3-dihydroperimidine with αα′-dibromo-o-xylene led, surprisingly, to (12) and 5-(2-propyl)benzo[g]naphtho[1,8-bc]-1,5-diazabicyclo[4.3.0]nonane (24).

Synthesis of medium-ring bicyclic bridgehead diamines from monocyclic diamines via α-aminoammonium ions

Abstract Condensation of 4-chlorobutanal and 5-chloropentanal with six cyclic diamines gave twelve α-aminoammonium salts; cleavage of these with LiAlH 4 gave medium-ring bicyclic diamines.

Reaction of a stable N ∴ N bonded radical cation with free radicals generated by pulse radiolysis: exceedingly rapid hydrogen abstraction from C–H bonds

Absolute rate constants have been measured for the reaction of the N ∴ N three-electron bonded 1,6-diazabicyclo[4.4.4]dodecane radical cation ([4.4.4]+˙) with various free radicals produced by means of pulse radiolysis. Reduction and oxidation reactions occur with rate constants generally somewhat below the diffusion limit. This is considered to reflect the inwardly oriented structure of the [4.4.4]+˙. High rate constants (ca. 109 mol–1 dm3 s–1) have been measured for hydrogen-atom abstraction from [4.4.4]+˙ by almost all radicals except eeq–. The most remarkable of these reactions appears to be H-atom abstraction by a thiyl radical [(CH3)3CS˙], which occurs with k 3.2 × 109 mol–1 dm3 s–1. This indicates highly labile C–H bonds in [4.4.4]+˙, which are considered to be those located on CH2 groups α to the nitrogen atoms. The fast radical–radical H-atom transfer is considered to be energetically assisted by favourable stereoelectronics and least heavy atom motion.

A case of 2π+2π cycloaddition of two enolate ions at ambient temperature

Abstract Reaction of two equivalents of 1-lithio-3,4-dihydronaphthalene with acenaphthenequinone between 0°C and 20°C leads to a derivative of tricyclo[4.3.0.05,9]nonane by di-oxy-Cope rearrangement followed by the unprecedented ”criss-cross“ 2π + 2π cycloaddition of the two enolate ions formed.

Synthesis of medium-ring bicyclic diamines by the alkylation and cleavage of cyclic amidines

Abstract 1,6-Diazabicyclo[4.3.3]dodecane ( 7 ), 1,6-diazabicyclo[4.3.2]undecane ( 8 ) and 1,8-diazabicyclo[6.3.3]tridecane ( 9 ) have been made by reduction of tricyclic α-aminoammonium salts with LiAlH 4 ; the protonation and oxidation of 8 and 9 are discussed.

A New Class of Remote N‐Heterocyclic Carbenes with Exceptionally Strong σ‐Donor Properties: Introducing Benzo[c]quinolin‐6‐ylidene

We make the case for benzo[c]quinolin-6-ylidene (1) as a strongly electron-donating carbene ligand. The facile synthesis of 6-trifluoromethanesulfonylbenzo[c]quinolizinium trifluoromethanesulfonate (2) gives straightforward access to a useful precursor for oxidative addition to low-valent metals, to yield the desired carbene complexes. This concept has been achieved in the case of [Mn(benzo[c]quinolin-6-ylidene)(CO)5](+) (15) and [Pd(benzo[c]quinolin-6-ylidene)(PPh3)2(L)](2+) L = THF (21), OTf (22) or pyridine (23). Attempts to coordinate to nickel result in coupling products from two carbene precursor fragments. The CO IR-stretching-frequency data for the manganese compound suggests benzo[c]quinolin-6-ylidene is at least as strong a donor as any heteroatom-stabilised carbene ligand reported.