Method for directed catalytic functionalization of alcohols

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. Provisional Application Ser. No. 62/141,093, having the title “METHOD FOR DIRECTED CATALYTIC FUNCTIONALIZATION OF ALCOHOLS”, filed on Mar. 31, 2015, the disclosure of which is incorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under contract NSF-CHE-1339674 awarded by the National Science Foundation and the Environmental Protection Agency. The Government has certain rights in the invention.

BRIEF SUMMARY

The presently disclosed embodiments, as well as features and aspects thereof, are directed towards a process comprising reacting an alcohol, e.g., a benzylic alcohol of formula I:

wherein R₁, R₂, R₃ and R₄ are independently selected from the group consisting of hydrogen, halogen, alkyl, and aryl; or R₁ and R₂, or R₂ and R₃, or R₃ and R₄ may independently together form an aryl ring;
each R₁₁ and R₁₂ is independently selected from the group consisting of hydrogen and alkyl;
and
n is 1, 2, or 3;
with an acetal of formula II:

wherein R₅, R₆, and R₇ are independently selected from the group consisting of hydrogen, halogen, and alkyl; or R₆, and R₇ may together form an aryl ring; and R₁₃ is alkyl; to provide the compound of formula III:

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₁₁, R₁₂, and n are as recited above;
and reacting the compound of formula III with the unsaturated compound of formula IV:

wherein R₈ and R₉ are independently selected from the group consisting of hydrogen and alkyl; and
R₁₀ is selected from the group consisting of cyano, nitro, CHO, CO(alkyl), COO(alkyl), CON H₂, CONH(alkyl), CON(alkyl)₂, wherein each alkyl is selected independent of another alkyl, and aryl; in the presence of a transition metal catalyst, and optionally in the presence of a ligand, and optionally in the presence of a silver salt, and optionally in the presence of a base to provide the compound of formula V:

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, and n are as recited above;
wherein the compound of formula V is reacted with an acid and an alcohol of formula R₁₃OH to provide a) the compound of formula VI:

wherein R₁, R₂, R₃, R₄, R₈, R₉, R₁₀, R₁₁, R₁₂, and n are as recited above; and b) the compound of formula II.
The presently disclosed embodiments, as well as features and aspects thereof, are directed towards a process comprising reacting an alcohol, e.g., a benzylic alcohol of formula I:

wherein R₁, R₂, R₃ and R₄ are independently selected from the group consisting of hydrogen, halogen, alkyl, and aryl; or R₁ and R₂, or R₂ and R₃, or R₃ and R₄ may independently together form an aryl ring;
each R₁₁ and R₁₂ is independently selected from the group consisting of hydrogen and alkyl; and
n is 1, 2, or 3;
with an acetal of formula II:

wherein R₅, R₆, and R₇ are independently selected from the group consisting of hydrogen, halogen, and alkyl; or R₆, and R₇ may together form an aryl ring; and R₁₃ is alkyl; to provide the compound of formula III:

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₁₁, R₁₂, and n are as recited above;
and reacting the compound of formula III with a compound of formula IVa:

in the presence of a transition metal catalyst, and optionally in the presence of a ligand, and optionally in the presence of a silver salt, and optionally in the presence of a base to provide the compound of formula Va:

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₁₁, R₁₂, and n are as recited above;
wherein the compound of formula Va is reacted with an acid and an alcohol of formula R₁₃OH to provide a) the compound of formula VIa:

wherein R₁, R₂, R₃, R₄, R₁₁, R₁₂, and n are as recited above; and b) the compound of formula II.

The present embodiments also include the compound of formula II, the compound of formula III, the compound of formula V, the compound of formula Va, the compound of formula VI, and the compound of formula VIa.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates Scheme 1.

FIGS. 2A and 2B illustrate Scheme 2.

FIG. 3 illustrates Scheme 3.

FIG. 4 illustrates Scheme 4.

FIG. 5 illustrates Scheme 5.

FIGS. 6A-6C illustrates Scheme 6a.

FIG. 7 illustrates Scheme 7.

FIG. 8 illustrates Scheme 7a.

FIG. 9 illustrates Scheme 7b.

FIG. 10 illustrates Scheme 8.

DETAILED DESCRIPTION

Aspects, features and advantages of several exemplary embodiments of the present invention will become better understood with regard to the following description in connection with the accompanying drawing(s). It should be apparent to those skilled in the art that the described embodiments of the present invention provided herein are illustrative only and not limiting, having been presented by way of example only. All features disclosed in this description may be replaced by alternative features serving the same or similar purpose, unless expressly stated otherwise. Therefore, numerous other embodiments of the modifications thereof are contemplated as falling within the scope of the present invention as defined herein and equivalents thereto. Hence, use of absolute terms such as, for example, “will,” “will not,” “shall,” “shall not,” “must” and “must not” are not meant to limit the scope of the present invention as the embodiments disclosed herein are merely exemplary.

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as exclusive, preferred or advantageous over other aspects.

Alkyl means C₁-C₁₂ alkyl, optionally substituted by one or more halogen; or alkyl means C₁-C₆ alkyl, optionally substituted by one or more halogen; or alkyl means C₁-C₃ alkyl, optionally substituted by one or more halogen.

Alkyl may be methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, each independently and optionally substituted by one or more halogen.

R₁₁ and R₁₂ may both be hydrogen; or R₁₁ is methyl and R₁₂ is hydrogen; R₁₁ and R₁₂ may both be methyl.

Aryl or “Ar” means a carbocyclic or heterocyclic aromatic ring that is optionally substituted or fused with another ring.

Ar in the compounds of formula IVa, Va, and VIa may be substituted by one or more alkyl, O-alkyl, COOalkyl, and/or haloalkyl.

In scheme 7 and 7a, the starting benzyl alcohols may be substituted ortho to the benzylic alcohol by haloalkyl, O-alkyl, nitro, or aryl.

“PyA” and “QuA” are defined in Scheme 5.

Halogen means fluorine, chlorine, bromine or iodine.

Transition metal means Paladium, Rhodium, or Ruthenium. Transition metal catalysts include Pd(OAc)₂ or a Rhodium acetate, or salt thereof, or a Ruthenium acetate, or a salt thereof. The amount of the transition metal catalyst may be from about 5 mol % to about 50 mol %, or from about 10 mol % to about 40 mol %, or from about 10 mol % to about 40 mol %, or from about 10 mol % to about 30 mol %.

In an embodiment, the process may further comprise a metal catalyst ligand. The ligand may be carboxylic acid, a peptide, e.g., a dipeptide or tripeptide with a carboxylic acid functional group. Examples of a ligand include N-acetyl-isoLeucine (Ac-Ile-OH, CAS Reg. No. 3077-46-1); N-acetyl-tert-butylleucine (Ac-tert-Leu-OH); and N-acetyl glycine (Ac-Gly-OH, CAS Reg, No. 543-24-8). The amount of the ligand may be from about 5 mol % to about 50 mol %, or from about 10 mol % to about 40 mol %, or from about 20 mol % to about 40 mol %, or from about 20 mol % to about 30 mol %.

In an embodiment, the process may further comprise a silver salt, e.g., silver carbonate. The amount of the silver salt may be from about 0.1 to about 5 equivalents, or from about 0.5 to about 4 equivalents, or from about 1 to about 4 equivalents. The process comprising the transition metal may be effected in a fluorinated solvent, e.g., 1,1,1,3,3,3-hexafluoro-2-propanol. The process may be effected at a temperature of from ambient temperature, to about the boiling point of the solvent.

The term “rsm” means recovered starting material.

EXAMPLES

Example 1

Synthesis of Molecular Scaffold of Formula 18:

As shown in Scheme 1 (FIG. 1), pyridine 2,3-dicarboxylic acid was converted to the corresponding diester by esterification in acid. Controlled reduction with diisobutyl aluminum hydride provided hemiacetal 17. Reaction of hemiacetal 17 with gaseous hydrogen chloride in methanol provided the compound of formula 18.

Example 2

Use of Molecular Scaffold 18 to Functionalize Benzylic Alcohols:

As shown in Scheme 2 (FIG. 2), compound 2 was reacted with benzyl alcohol in the presence of 5 Å molecular sieves to provide the acetal 3 in 92% yield. Reaction of acetal 3 with ethyl acrylate in the presence of catalytic Pd(OAc)₂, 0.2 molar equivalents N-acetylglycine, and 3 molar equivalents of AgOAc as the oxidant in hexafluoroisopropanol at 90° C. provided mono-substituted adduct 5a and disubstituted adduct 5b. Reaction with methanol and hydrogen chloride provided compounds 6a and 6b. Reaction of 2-chlorobenzyl alcohol (8) and 2-methylbenzyl alcohol (7) under essentially same conditions afford solely the monosubstituted adducts 14 and 13, respectively.

In another embodiment, as shown in Scheme 3 (FIG. 3), the reaction sequence or process may be effected without isolation of any products. For example, Compound 6a was synthesized in the same manner as in Scheme 1 (FIG. 1) without purification of compound 3 or compound 5a to provide a 42% yield of compound 6a.

In another embodiment, the scaffold compound 2 may be recovered. Benzylic alcohol 9 was coupled with alkene 18 in the presence of Pd(OAc)₂ to provide compound 19. Compound 19 was treated with gaseous hydrogen chloride in methanol to yield alcohol 20 and compound 2 in high yields.

Example 3

Reaction of Phenyl-BPin (Table 1):

Reaction of one equivalent of 2-methylbenzylOPyA with PhBPin (3 equiv) under the catalysis of Pd(OAc)₂ (10 mol %) and Ac-Gly-OH (20 mol %), Ag₂CO₃ (1 equiv) and CsF (2 equiv) as the additives in HFIP (0.1 M) at 90° C. for 6 h, the desired product was afforded in 11% NMR yield, with 83% NMR yield of rsm (entry 1, Table 1).

Then Na₂CO₃ (2 equiv) gave the best result (34/3% mono/di, 51% rsm, entry 8, Table 1) among different bases. Reagent ratio and concentration shows that more oxidants (2 equiv), less base (1 equiv), and less concentration (0.05 M) gave a better result (43/4% mono/di, 38% rsm, entries 9-15, Table 1).

Other embodiments are provided in the examples of Schemes 4 and 6a (FIGS. 4 and 6).

Example 4

The residue QuA was prepared and attached to 2-methyl benzyl alcohol according to Scheme 7 (FIG. 7).

Example 5

When the QuA-attached benzyl alcohol was subjected to the coupling reaction (see substantially same conditions of Example 3), higher yield (69% NMR yield of mono) was achieved (entry 1, Table 2).

Interestingly, a second arylation of the new formed phenyl group could be afforded in 8% NMR yield, plus 17% rsm. After screening of different bases, K₂CO₃ (2 equiv) gave the best yield (75/14% mono/di, 6% rsm, entry 4, Table 2). Less amount of Pd(OAc)₂ (5 mol %) or lower temperature both led to decreased yields even with longer reaction time (entry 7, 9, Table 2). PhBF₃K showed lower reactivity than PhBPin (entry 10, Table 1). Benzoquinone and water, which were supposed to increase the reduction elimination rates, did not show any advantages in this chemistry (entry 11, 12, Table 2).

In studies on the effects of the ligands, Ac-Ile-OH turned out to be the best one (with a much better mono/di ratio, entry 16, Table 2). Ac-tert-Leu-OH gave the best mono/di ratio, but lower yield (entry 17, Table 2). Apparently bulky ligand can control the form of the di-product, but lead to a lower yield. Finally we chose entry 16 in Table 2 as the optimized conditions for further studies.

With reference to Schemes 7a and 7b (FIGS. 8 and 9), the aryl group coupled may be substituted. Various substituted Ar-BPins (both electro-donating and electro-withdrawing substituted groups, such as OMe, CF₃, CO₂Me) were tolerated, affording the corresponding products in good to excellent yields. Moreover, 2-naphthylboronic acid pinacol ester was also tolerated, gave the corresponding mono product in 76% yield. Gratifyingly, ortho-substituents Ar-BPins still gave a good yield. Then a range of scaffold-attached benzylic alcohol substrates were evaluated. For ortho-substituted arenes, moderate to good yields of the biaryls were formed. For cases without substituted groups at the ortho-position, both mono- and di-biaryls were observed. Homo-benzyl alcohol was tolerated in this transformation, affording the corresponding product in 83% yield. But bishomobenzylic alcohol substrate shows low reactivity with only 11% NMR yield, plus 77% rsm. A secondary alcohol-based substrate was reactive, which shows mono-selectivity.

With reference to Scheme 8 (FIG. 10), two steps with only one purification gave the biaryl alcohol in 89% yield, with the scaffold recovered in 86% yield, highlighting the utility of this scaffold. Furthermore, benzylic alcohol could be converted to the arylation product without any intermediary purification (59% yield, 35% rsm of benzylic alcohol, 73% recovery of the scaffold based on BzOQuA), but for the arylation step, reaction was failed to go completion, probably due to the quinoline-based impurities from the first step.

Therefore, although selected aspects have been illustrated and described in detail, it will be understood that various substitutions and alterations may be made therein without departing from the spirit and scope of the present invention, as defined by the following claims.