Carlos G. Gutierrez

Improving Underrepresented Minority Student Persistence in STEM

Members of the Joint Working Group on Improving Underrepresented Minorities (URMs) Persistence in Science, Technology, Engineering and Mathematics (STEM), utilizing Kurt Lewin’s planned approach to change, describe five recommendations to increase URM persistence in STEM at the undergraduate level.

A MUCH IMPROVED SYNTHESIS OF THE SIDEROPHORE ENTEROBACTIN

Abstract Enterobactin, the cyclic trimer of N-(2,3-dihydroxybenzoyl)-L-serine has been efficiently prepared. A simple and high yield procedure has been developed for construction of N-protected serine trilactone as the key intermediate: methyl N-trityl-L-serinate and 2,2-dibutyl-1,3,2-dioxastannolane were refluxed in xylene to produce the triolide as the only lactone product in 85% yield.

Selective desulfurization of 1,3-dithianes, -oxathiolanes and -thiazolidines by tributyltin hydride

Abstract Selective desulfurization of 2-alkyl-1,3-dithianes, -oxathiolanes, or -thiazolidines 1 with one equivalent of tri-n-butyltin hydride yields acyclic compounds R1R2CHX(CH2)nSSnBu3 (X = S,O,NH; n= 2,3), (2) which can be destannylated to the corresponding mercaptans 3.

Substituted diether diols by ring-opening of carbocyclic and stannylene acetals

Reduction of malonaldehyde bis(ethylene and propylene acetals) with borane or monochloroborane produces diether diols 1 and 2 in high yield. Similar reduction of glyoxal bis(ethylene acetals) has only limited utility for the preparation of tetrasubstituted triethylene glycols 3. Organotin chemistry is complementary: stannylene acetals prepared from disubstituted vicinal diols can be alkylated with half an equivalent of 1,2-dibromoethane to produce tetrasubstituted triethylene glycols 3, or with two equivalents of 2-chloroethanol to produce disubstituted triethylene glycols 4.

SUBSTITUTED TRIETHYLENE GLYCOLS FROM DIBUTYLSTANNYLENE ACETALS

Abstract Stannylene acetals prepared from disubstituted vicinal diols can be alkylated with a half equivalent of 1,2-dibromoethane to produce tetrasubstituted triethylene glycols 2 , or with two equivalents of 2-chloroethanol to produce disubstituted triethylene glycols 1 .

POLYDENTATE SNXM (X = S,O,N) LIGANDS BY SELECTIVE REDUCTION OF ORGANOSULFUR HETEROCYCLES WITH TRIBUTYLTIN HYDRIDE

Abstract Acyclic tetradentate organosulfur ligands of the type S2X2 (where X = S.O.N) can be efficiently prepared by selective desulfurization of bis(1,3-dithiolanes) and bis(1,3-dithianes); bis(1,3-oxathiolanes); and bis(thiazolidines) with two equivalents of tri-n-butyltin hydride. This is a very versatile procedure as many dialdehydes and diketones (or their synthetic equivalents) are available for elaboration into bis(thioheterocycles) by reaction with 1,2-ethane- and 1,3-propanedithiols, mercaptoethanol or mercaptoethylamine, and their varied structural features can be incorporated into S2X2 ligands. The net result of the procedure is the controlled formal monoalkylation of dithiols to form compounds 1 (X = S); and the alkylation of the less nucleophilic heteroatom (O or N) of mercaptoethanol or mercaptoethylamine to form 1 (X = O,N).

REDUCTION OF THIONOESTERS TO ETHERS BY TRIORGANOTIN HYDRIDES

Abstract Esters 1 are efficiently deoxygenated to the corresponding ethers 3 in two steps by first conversion to the thionoesters 2 and subsequent reduction of these by triorganotin hydrides.

New synthesis of tetradentate organosulphur ligands by organotin reduction of bis(dithiolanes)

Tetradentate organosulphur ligands are efficiently prepared by the selective reduction of bis(dithiolanes) with two equivalents of tri-n-butyltin hydride.