Reductions of conjugated carbonyl compounds with cyanoborohydride in acidic media

Abstract

The reductions of a variety of conjugated aldehydes and ketones with NaBHaCN in acidic methanol and hexamethylphosphortriamide (HMPT) have been investigated. Alicyclic carbonyl compounds afforded principally the corresponding allylic alcohols in both solvents with methyl ethers as side products in methanol. The introduction of additional conjugation often resulted in reduction to allylic hydrocarbons, presumably via acid-induced ionization and hydride trapping. Formation of saturated alcohols was not observed in any alicyclic cases studied. Cyclic enones, on the other hand, gave mixtures of allylic and saturated alcohols resulting from competing 1,2 and 1,4 addition of cyanoborohydride.

Wet SiO2As a Suitable Media for Fast and Efficient Reduction of Carbonyl Compounds with NaBH3CN under Solvent-Free and Acid-Free Conditions

“…6 It was also reported that doing of the reductions in acidic HMPT produces allylic hydrocarbons accompanied with allyl alcohols. 6 Thus, reduction of conjugated carbonyl compounds with NaBH3CN in acidic protic and aprotic solvents is not regioselective and it suffers from harsh reaction conditions (strongly acidic media) accompanied with side product formation.…”

“…As seen in Table 1, NaBH3CN exhibited the best reducing capability in the presence of wet SiO2 under solvent-free conditions. However, 0.2 g wet SiO2 (100 m/m, mass ratio) which is prepared by simply mixing of water (0.1 g) and SiO 2 (0.1 g) was the requirement for complete reduction of PhCHO at room temperature or oil bath conditions (entries 5,6).…”

“…Thus in basic or neutral media, aldehydes and ketones are practically inert toward the reagent and adequate reduction rates are only obtained under acidic conditions (pH 3 -4). 5,6 Although, NaBH3CN has been used in many organic reactions, however, this reagent suffers from harsh reaction conditions (strong acidic media), limitation to use acid-sensitive functional groups and formation of side products.…”

Radical Reduction of Epoxides Using a Titanocene(III)/Water System: Synthesis of β‐Deuterated Alcohols and Their Use as Internal Standards in Food Analysis

“…[26a] 22, [30] 23, [31] 24, [32] 25, [33] 26, [34] 27, [35] 28, [36] 31-d 1 , [37] 32, [38] 33, [18] 34, [19] and 1-d 1 .…”

Chapter 13. Synthetic methods

“…This route is distinguished by its use of the enol phosphinate (66) as precursor for the regiospecific formation of the enolate (67), which is trapped with formaldehyde, leading to hydroxymethylcyclopentenone (68). Elimination of water followed by conjugate addition of a vinylcuprate to enone (69) and subsequent elaboration of the fully functionalized cyclopentanone then completes a new total synthesis of PGF,,. Lithium di-(a-methoxyviny1)cuprate (71), another masked anion, prepared from a-methoxyvinyl-lithium, has been shown to undergo conjugate addition reactions to …”