Nucleic acid related compounds. 70. Synthesis of 2'(and 3')-deoxy-2'(and 3')-methyleneadenosines and bis(methylene)furan 4',5'-didehydro-5'-deoxy-2'(and 3')-methyleneadenosines. Inhibitors of S-adenosyl-L-homocysteine hydrolase and ribonucleotide reductase